auto merge of #8832 : alexcrichton/rust/fix-libuv-build, r=pcwalton
auto merge of #8832 : alexcrichton/rust/fix-libuv-build, r=pcwalton

It turns out that gyp (libuv's new build system) wants x64 for a 64-bit x86
architecture and ia32 for a 32-bit architecture, so this performs the relevant
mapping and then invokes libuv's configure script with the appropriate target
architecture.

This can be verified by running make with VERBOSE=1 and seeing that beforehand
on a 64-bit build libuv was passed "-arch i386" and now it's passed
"-arch x86_64"

Closes #8826

omasanori/rust,carols10cents/rust,GBGamer/rust,defuz/rust,mahkoh/rust,stepancheg/rust-ide-rust,mvdnes/rust,pczarn/rust,ruud-v-a/rust,mdinger/rust,victorvde/rust,richo/rust,aepsil0n/rust,aidancully/rust,KokaKiwi/rust,SiegeLord/rust,michaelballantyne/rust-gpu,robertg/rust,hauleth/rust,carols10cents/rust,ejjeong/rust,rprichard/rust,mahkoh/rust,omasanori/rust,aidancully/rust,mihneadb/rust,mihneadb/rust,miniupnp/rust,zachwick/rust,kwantam/rust,dinfuehr/rust,richo/rust,pshc/rust,GrahamDennis/rand,avdi/rust,vhbit/rust,stepancheg/rust-ide-rust,fabricedesre/rust,Ryman/rust,sae-bom/rust,gifnksm/rust,sae-bom/rust,dinfuehr/rust,hauleth/rust,quornian/rust,aepsil0n/rust,Ryman/rust,aneeshusa/rust,0x73/rust,pelmers/rust,jbclements/rust,nwin/rust,fabricedesre/rust,dwillmer/rust,aturon/rust,P1start/rust,emk/rust,barosl/rust,ruud-v-a/rust,ebfull/rust,nwin/rust,zubron/rust,ruud-v-a/rust,miniupnp/rust,pshc/rust,ebfull/rust,krzysz00/rust,aturon/rust,pczarn/rust,andars/rust,mahkoh/rust,ktossell/rust,pshc/rust,richo/rust,arthurprs/rand,reem/rust,jbclements/rust,huonw/rand,krzysz00/rust,pshc/rust,dwillmer/rust,zubron/rust,AerialX/rust,bombless/rust,nwin/rust,avdi/rust,pythonesque/rust,erickt/rust,barosl/rust,XMPPwocky/rust,Ryman/rust,aturon/rust,aturon/rust,LeoTestard/rust,seanrivera/rust,untitaker/rust,miniupnp/rust,LeoTestard/rust,andars/rust,ruud-v-a/rust,erickt/rust,nham/rust,KokaKiwi/rust,l0kod/rust,ebfull/rust,erickt/rust,bhickey/rand,SiegeLord/rust,emk/rust,l0kod/rust,sae-bom/rust,zubron/rust,mitsuhiko/rust,rprichard/rust,ktossell/rust,kwantam/rust,pythonesque/rust,shepmaster/rand,nham/rust,seanrivera/rust,defuz/rust,pelmers/rust,omasanori/rust,0x73/rust,jbclements/rust,emk/rust,zubron/rust,reem/rust,TheNeikos/rust,graydon/rust,mitsuhiko/rust,ejjeong/rust,nwin/rust,mvdnes/rust,kwantam/rust,robertg/rust,hauleth/rust,victorvde/rust,hauleth/rust,carols10cents/rust,untitaker/rust,pythonesque/rust,stepancheg/rust-ide-rust,philyoon/rust,seanrivera/rust,emk/rust,AerialX/rust,AerialX/rust-rt-minimal,AerialX/rust-rt-minimal,XMPPwocky/rust,mdinger/rust,sae-bom/rust,zachwick/rust,aidancully/rust,bombless/rust,jroesch/rust,seanrivera/rust,0x73/rust,jashank/rust,quornian/rust,TheNeikos/rust,barosl/rust,ebfull/rust,untitaker/rust,waynenilsen/rand,P1start/rust,dwillmer/rust,stepancheg/rust-ide-rust,kwantam/rust,bombless/rust,P1start/rust,stepancheg/rust-ide-rust,graydon/rust,defuz/rust,ruud-v-a/rust,gifnksm/rust,mitsuhiko/rust,servo/rust,stepancheg/rust-ide-rust,philyoon/rust,pczarn/rust,Ryman/rust,jroesch/rust,jashank/rust,aturon/rust,jashank/rust,philyoon/rust,sae-bom/rust,victorvde/rust,l0kod/rust,graydon/rust,erickt/rust,rprichard/rust,aneeshusa/rust,jashank/rust,erickt/rust,ebfull/rust,vhbit/rust,SiegeLord/rust,mvdnes/rust,l0kod/rust,GBGamer/rust,rohitjoshi/rust,retep998/rand,rohitjoshi/rust,aturon/rust,defuz/rust,victorvde/rust,mitsuhiko/rust,pczarn/rust,LeoTestard/rust,seanrivera/rust,jroesch/rust,mihneadb/rust,LeoTestard/rust,pshc/rust,robertg/rust,dinfuehr/rust,P1start/rust,AerialX/rust-rt-minimal,mvdnes/rust,AerialX/rust,jbclements/rust,omasanori/rust,dwillmer/rust,victorvde/rust,XMPPwocky/rust,pelmers/rust,dinfuehr/rust,ejjeong/rust,michaelballantyne/rust-gpu,GBGamer/rust,servo/rust,krzysz00/rust,cllns/rust,ktossell/rust,nwin/rust,rohitjoshi/rust,miniupnp/rust,TheNeikos/rust,dwillmer/rust,michaelballantyne/rust-gpu,0x73/rust,GBGamer/rust,GBGamer/rust,pythonesque/rust,servo/rust,andars/rust,mahkoh/rust,ejjeong/rust,AerialX/rust-rt-minimal,zubron/rust,jroesch/rust,robertg/rust,bombless/rust,philyoon/rust,carols10cents/rust,robertg/rust,zachwick/rust,AerialX/rust,AerialX/rust-rt-minimal,erickt/rust,untitaker/rust,achanda/rand,vhbit/rust,pelmers/rust,ebfull/rand,quornian/rust,jroesch/rust,jashank/rust,GBGamer/rust,emk/rust,jroesch/rust,mitsuhiko/rust,pczarn/rust,ruud-v-a/rust,zachwick/rust,cllns/rust,TheNeikos/rust,pshc/rust,barosl/rust,bombless/rust,stepancheg/rust-ide-rust,sae-bom/rust,TheNeikos/rust,jashank/rust,pczarn/rust,AerialX/rust-rt-minimal,zachwick/rust,kimroen/rust,michaelballantyne/rust-gpu,fabricedesre/rust,jroesch/rust,jashank/rust,SiegeLord/rust,ktossell/rust,quornian/rust,mihneadb/rust,GBGamer/rust,ktossell/rust,mdinger/rust,Ryman/rust,rprichard/rust,avdi/rust,quornian/rust,carols10cents/rust,pythonesque/rust,P1start/rust,nham/rust,aepsil0n/rust,Ryman/rust,robertg/rust,kimroen/rust,fabricedesre/rust,rprichard/rust,defuz/rust,servo/rust,servo/rust,rprichard/rust,gifnksm/rust,mahkoh/rust,krzysz00/rust,andars/rust,AerialX/rust,SiegeLord/rust,aepsil0n/rust,richo/rust,mdinger/rust,miniupnp/rust,dwillmer/rust,vhbit/rust,servo/rust,graydon/rust,KokaKiwi/rust,hauleth/rust,zaeleus/rust,fabricedesre/rust,LeoTestard/rust,krzysz00/rust,zubron/rust,P1start/rust,michaelballantyne/rust-gpu,mvdnes/rust,zubron/rust,vhbit/rust,pelmers/rust,vhbit/rust,dwillmer/rust,gifnksm/rust,cllns/rust,ejjeong/rust,mihneadb/rust,pelmers/rust,Ryman/rust,fabricedesre/rust,KokaKiwi/rust,dwillmer/rust,reem/rust,ejjeong/rust,cllns/rust,GBGamer/rust,Aeri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