auto merge of #11215 : alexcrichton/rust/metadata-filename, r=pcwalton
auto merge of #11215 : alexcrichton/rust/metadata-filename, r=pcwalton

Right now if you have concurrent builds of two libraries in the same directory
(such as rustc's bootstrapping process), it's possible that two libraries will
stomp over each others' metadata, producing corrupt rlibs.

By placing the metadata file in a tempdir we're guranteed to not conflict with
ay other builds happening concurrently. Normally this isn't a problem because
output filenames are scoped to the name of the crate, but metadata is special in
that it has the same name across all crates.

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