Look for aapt in platform specific directories.
Look for aapt in platform specific directories.

Summary:
The buckconfig value should point to a directory that contains the aapt
binaries in platform specific sub-directories (linux/mac/windows).

Test Plan:
In fbandroid:
$ mkdir -p aapt/linux
$ ln -s /home/natthu/devtools/aosp/out/host/linux-x86/bin/aapt aapt/linux/aapt

Edit .buckconfig tools section
```
[tools]
    proguard = proguard/proguard-fork.jar
    aapt = aapt
```

$ buck build instagram

Inspect chrome trace and verify overridden aapt is used.

illicitonion/buck,zhan-xiong/buck,clonetwin26/buck,romanoid/buck,zpao/buck,shybovycha/buck,romanoid/buck,k21/buck,mikekap/buck,OkBuilds/buck,Distrotech/buck,saleeh93/buck-cutom,SeleniumHQ/buck,rmaz/buck,brettwooldridge/buck,zhan-xiong/buck,Dominator008/buck,1yvT0s/buck,Heart2009/buck,mogers/buck,janicduplessis/buck,Distrotech/buck,dsyang/buck,hgl888/buck,davido/buck,Learn-Android-app/buck,rhencke/buck,rhencke/buck,ilya-klyuchnikov/buck,vschs007/buck,shs96c/buck,SeleniumHQ/buck,liuyang-li/buck,rowillia/buck,pwz3n0/buck,shs96c/buck,MarkRunWu/buck,justinmuller/buck,robbertvanginkel/buck,dushmis/buck,stuhood/buck,janicduplessis/buck,sdwilsh/buck,zhan-xiong/buck,nguyentruongtho/buck,lukw00/buck,Addepar/buck,pwz3n0/buck,kageiit/buck,siddhartharay007/buck,artiya4u/buck,Distrotech/buck,marcinkwiatkowski/buck,tgummerer/buck,sdwilsh/buck,daedric/buck,mikekap/buck,janicduplessis/buck,daedric/buck,dushmis/buck,sdwilsh/buck,hgl888/buck,pwz3n0/buck,tgummerer/buck,tgummerer/buck,romanoid/buck,Addepar/buck,Heart2009/buck,shybovycha/buck,dsyang/buck,shybovycha/buck,Learn-Android-app/buck,mogers/buck,sdwilsh/buck,dsyang/buck,facebook/buck,illicitonion/buck,marcinkwiatkowski/buck,bocon13/buck,romanoid/buck,raviagarwal7/buck,vine/buck,siddhartharay007/buck,stuhood/buck,marcinkwiatkowski/buck,luiseduardohdbackup/buck,Addepar/buck,saleeh93/buck-cutom,janicduplessis/buck,liuyang-li/buck,dsyang/buck,clonetwin26/buck,grumpyjames/buck,LegNeato/buck,vine/buck,dpursehouse/buck,facebook/buck,rmaz/buck,zpao/buck,mogers/buck,JoelMarcey/buck,sdwilsh/buck,zhuxiaohao/buck,Addepar/buck,liuyang-li/buck,dpursehouse/buck,dushmis/buck,rmaz/buck,mogers/buck,OkBuilds/buck,davido/buck,nguyentruongtho/buck,darkforestzero/buck,ilya-klyuchnikov/buck,clonetwin26/buck,mnuessler/buck,OkBuilds/buck,SeleniumHQ/buck,facebook/buck,clonetwin26/buck,bocon13/buck,Learn-Android-app/buck,JoelMarcey/buck,k21/buck,hgl888/buck,mnuessler/buck,neonichu/buck,rhencke/buck,OkBuilds/buck,siddhartharay007/buck,SeleniumHQ/buck,OkBuilds/buck,shybovycha/buck,rmaz/buck,zhan-xiong/buck,Dominator008/buck,romanoid/buck,justinmuller/buck,pwz3n0/buck,shs96c/buck,vschs007/buck,shs96c/buck,k21/buck,daedric/buck,shybovycha/buck,SeleniumHQ/buck,janicduplessis/buck,sdwilsh/buck,romanoid/buck,hgl888/buck,1yvT0s/buck,mogers/buck,zhan-xiong/buck,dpursehouse/buck,liuyang-li/buck,shs96c/buck,rowillia/buck,justinmuller/buck,romanoid/buck,vschs007/buck,robbertvanginkel/buck,bocon13/buck,dpursehouse/buck,artiya4u/buck,mread/buck,mikekap/buck,neonichu/buck,artiya4u/buck,zhan-xiong/buck,darkforestzero/buck,marcinkwiatkowski/buck,ilya-klyuchnikov/buck,rhencke/buck,Addepar/buck,shs96c/buck,sdwilsh/buck,bocon13/buck,shybovycha/buck,grumpyjames/buck,raviagarwal7/buck,dsyang/buck,neonichu/buck,siddhartharay007/buck,pwz3n0/buck,clonetwin26/buck,romanoid/buck,rmaz/buck,vschs007/buck,1yvT0s/buck,davido/buck,mogers/buck,lukw00/buck,stuhood/buck,davido/buck,luiseduardohdbackup/buck,LegNeato/buck,shs96c/buck,liuyang-li/buck,darkforestzero/buck,janicduplessis/buck,vine/buck,sdwilsh/buck,siddhartharay007/buck,justinmuller/buck,OkBuilds/buck,nguyentruongtho/buck,zhan-xiong/buck,dushmis/buck,dsyang/buck,liuyang-li/buck,artiya4u/buck,daedric/buck,luiseduardohdbackup/buck,lukw00/buck,1yvT0s/buck,robbertvanginkel/buck,romanoid/buck,OkBuilds/buck,ilya-klyuchnikov/buck,shs96c/buck,robbertvanginkel/buck,mnuessler/buck,grumpyjames/buck,MarkRunWu/buck,janicduplessis/buck,lukw00/buck,nguyentruongtho/buck,darkforestzero/buck,ilya-klyuchnikov/buck,brettwooldridge/buck,bocon13/buck,rmaz/buck,grumpyjames/buck,1yvT0s/buck,Learn-Android-app/buck,janicduplessis/buck,Distrotech/buck,brettwooldridge/buck,clonetwin26/buck,JoelMarcey/buck,lukw00/buck,LegNeato/buck,JoelMarcey/buck,k21/buck,Addepar/buck,zpao/buck,mogers/buck,tgummerer/buck,janicduplessis/buck,hgl888/buck,daedric/buck,ilya-klyuchnikov/buck,rowillia/buck,hgl888/buck,artiya4u/buck,zhan-xiong/buck,vschs007/buck,illicitonion/buck,rowillia/buck,shs96c/buck,marcinkwiatkowski/buck,robbertvanginkel/buck,robbertvanginkel/buck,justinmuller/buck,daedric/buck,daedric/buck,justinmuller/buck,kageiit/buck,zhan-xiong/buck,darkforestzero/buck,raviagarwal7/buck,SeleniumHQ/buck,clonetwin26/buck,neonichu/buck,rmaz/buck,vine/buck,darkforestzero/buck,pwz3n0/buck,1yvT0s/buck,brettwooldridge/buck,SeleniumHQ/buck,zhuxiaohao/buck,clonetwin26/buck,janicduplessis/buck,justinmuller/buck,rhencke/buck,lukw00/buck,daedric/buck,k21/buck,LegNeato/buck,vine/buck,rhencke/buck,Addepar/buck,kageiit/buck,davido/buck,Addepar/buck,zhuxiaohao/buck,clonetwin26/buck,Distrotech/buck,OkBuilds/buck,lukw00/buck,luiseduardohdbackup/buck,raviagarwal7/buck,vschs007/buck,zhuxiaohao/buck,daedric/buck,dpursehouse/buck,ilya-klyuchnikov/buck,brettwooldridge/buck,mikekap/buck,raviagarwal7/buck,Distrotech/buck,dpursehouse/buck,mikekap/buck,SeleniumHQ/buck,clonetwin26/buck,Distrotech/buck,grumpyjames/buck,vine/buck,illicitonion/buck,nguyentruongtho/buck,ilya-klyuchnikov/buck,Addepar/buck,dushmis/buck,hgl888/buck,mogers/buck,liuyang-li/buck,vschs007/buck,illicitonion/buck,ilya-klyuchnikov/buck,mnuessler/buck,davido/buck,Addepar/buck,pwz3n0/buck,raviagarwal7/buck,raviagarwal7/buck,vine/buck,Heart2009/buck,justinmuller/buck,illicitonion/buck,sdwilsh/buck,robbertvanginkel/buck,Learn-Android-app/buck,stuhood/buck,sdwilsh/buck,1yvT0s/buck,liuyang-li/buck,justinmuller/buck,mnuessler/buck,romanoid/buck,justinmuller/buck,vschs007/buck,shs96c/buck,pwz3n0/buck,dushmis/buck,lukw00/buck,raviagarwal7/buck,saleeh93/buck-cutom,LegNeato/buck,darkforestzero/buck,kageiit/buck,davido/buck,davido/buck,mikekap/buck,bocon13/buck,marcinkwiatkowski/buck,nguyentruongtho/buck,dushmis/buck,dpursehouse/buck,MarkRunWu/buck,OkBuilds/buck,Heart2009/buck,MarkRunWu/buck,shybovycha/buck,robbertvanginkel/buck,ilya-klyuchnikov/buck,vine/buck,vschs007/buck,SeleniumHQ/buck,brettwooldridge/buck,bocon13/buck,Addepar/buck,mnuessler/buck,stuhood/buck,ilya-klyuchnikov/buck,siddhartharay007/buck,davido/buck,romanoid/buck,davido/buck,LegNeato/buck,artiya4u/buck,dsyang/buck,k21/buck,dushmis/buck,saleeh93/buck-cutom,darkforestzero/buck,JoelMarcey/buck,Dominator008/buck,zhan-xiong/buck,marcinkwiatkowski/buck,sdwilsh/buck,romanoid/buck,rhencke/buck,saleeh93/buck-cutom,k21/buck,bocon13/buck,nguyentruongtho/buck,Dominator008/buck,rmaz/buck,Dominator008/buck,vine/buck,zhuxiaohao/buck,luiseduardohdbackup/buck,kageiit/buck,liuyang-li/buck,raviagarwal7/buck,brettwooldridge/buck,brettwooldridge/buck,siddhartharay007/buck,daedric/buck,mikekap/buck,bocon13/buck,raviagarwal7/buck,romanoid/buck,vschs007/buck,JoelMarcey/buck,stuhood/buck,robbertvanginkel/buck,vschs007/buck,artiya4u/buck,k21/buck,LegNeato/buck,marcinkwiatkowski/buck,LegNeato/buck,rowillia/buck,mread/buck,kageiit/buck,lukw00/buck,stuhood/buck,Distrotech/buck,luiseduardohdbackup/buck,mikekap/buck,tgummerer/buck,OkBuilds/buck,Heart2009/buck,rmaz/buck,dsyang/buck,zhan-xiong/buck,rhencke/buck,marcinkwiatkowski/buck,facebook/buck,darkforestzero/buck,liuyang-li/buck,raviagarwal7/buck,mogers/buck,artiya4u/buck,illicitonion/buck,MarkRunWu/buck,tgummerer/buck,neonichu/buck,bocon13/buck,Distrotech/buck,shybovycha/buck,daedric/buck,illicitonion/buck,siddhartharay007/buck,rowillia/buck,zhuxiaohao/buck,siddhartharay007/buck,mogers/buck,stuhood/buck,Addepar/buck,OkBuilds/buck,tgummerer/buck,janicduplessis/buck,Heart2009/buck,LegNeato/buck,k21/buck,sdwilsh/buck,rmaz/buck,darkforestzero/buck,luiseduardohdbackup/buck,shs96c/buck,mnuessler/buck,MarkRunWu/buck,mikekap/buck,JoelMarcey/buck,grumpyjames/buck,marcinkwiatkowski/buck,dsyang/buck,Dominator008/buck,robbertvanginkel/buck,marcinkwiatkowski/buck,pwz3n0/buck,justinmuller/buck,JoelMarcey/buck,artiya4u/buck,1yvT0s/buck,raviagarwal7/buck,neonichu/buck,zhan-xiong/buck,Learn-Android-app/buck,bocon13/buck,grumpyjames/buck,justinmuller/buck,JoelMarcey/buck,pwz3n0/buck,marcinkwiatkowski/buck,tgummerer/buck,janicduplessis/buck,davido/buck,illicitonion/buck,1yvT0s/buck,luiseduardohdbackup/buck,LegNeato/buck,hgl888/buck,marcinkwiatkowski/buck,stuhood/buck,mikekap/buck,illicitonion/buck,k21/buck,rhencke/buck,vine/buck,rmaz/buck,illicitonion/buck,SeleniumHQ/buck,Learn-Android-app/buck,vschs007/buck,sdwilsh/buck,shybovycha/buck,robbertvanginkel/buck,Learn-Android-app/buck,darkforestzero/buck,SeleniumHQ/buck,dpursehouse/buck,LegNeato/buck,OkBuilds/buck,clonetwin26/buck,shybovycha/buck,clonetwin26/buck,zhuxiaohao/buck,mnuessler/buck,mread/buck,illicitonion/buck,illicitonion/buck,Dominator008/buck,Heart2009/buck,facebook/buck,k21/buck,neonichu/buck,grumpyjames/buck,k21/buck,grumpyjames/buck,liuyang-li/buck,rowillia/buck,saleeh93/buck-cutom,grumpyjames/buck,dsyang/buck,shs96c/buck,lukw00/buck,dsyang/buck,rhencke/buck,rowillia/buck,rmaz/buck,darkforestzero/buck,ilya-klyuchnikov/buck,JoelMarcey/buck,Dominator008/buck,mread/buck,brettwooldridge/buck,clonetwin26/buck,robbertvanginkel/buck,ilya-klyuchnikov/buck,tgummerer/buck,brettwooldridge/buck,tgummerer/buck,JoelMarcey/buck,zhuxiaohao/buck,shybovycha/buck,brettwooldridge/buck,Learn-Android-app/buck,Dominator008/buck,hgl888/buck,brettwooldridge/buck,rowillia/buck,neonichu/buck,justinmuller/buck,mikekap/buck,luiseduardohdbackup/buck,zhuxiaohao/buck,Heart2009/buck,JoelMarcey/buck,dushmis/buck,shybovycha/buck,SeleniumHQ/buck,SeleniumHQ/buck,facebook/buck,rowillia/buck,rowillia/buck,Heart2009/buck,OkBuilds/buck,robbertvanginkel/buck,kageiit/buck,tgummerer/buck,Dominator008/buck,pwz3n0/buck,Dominator008/buck,dushmis/buck,MarkRunWu/buck,mread/buck,dsyang/buck,Dominator008/buck,JoelMarcey/buck,vschs007/buck,rhencke/buck,brettwooldridge/buck,mread/buck,artiya4u/buck,Distrotech/buck,mikekap/buck,daedric/buck,LegNeato/buck,shs96c/buck,Distrotech/buck,lukw00/buck,daedric/buck,rowillia/buck,Learn-Android-app/buck,zpao/buck,MarkRunWu/buck,Addepar/buck,stuhood/buck,zhan-xiong/buck,grumpyjames/buck,davido/buck,neonichu/buck,shybovycha/buck,rmaz/buck,k21/buck,zpao/buck,mogers/buck,stuhood/buck,Learn-Android-app/buck,grumpyjames/buck,zpao/buck,darkforestzero/buck,LegNeato/buck,mnuessler/buck,bocon13/buck,zpao/buck,davido/buck,artiya4u/buck,raviagarwal7/buck,facebook/buck,vine/buck,dsyang/buck