Escape flags when passed to Xcode.
Escape flags when passed to Xcode.

Summary: Xcode passes the flags through the shell, so they need to be escaped.

Test Plan:
CI
Generate a project for a target that has a preprocessor define with special characters.

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