auto merge of #11742 : eminence/rust/dylib-test-fix, r=alexcrichton
auto merge of #11742 : eminence/rust/dylib-test-fix, r=alexcrichton

On my Gentoo Linux machine, the c-dynamic-dylib test is failing, because libcfoo can't be found.  bar has a correct rpath for finding libfoo.so, but libfoo.so's rpath doesn't contain the right entries for finding libcfoo.


Below is the test failure on my machine.  This test pass with this commit:

```
maketest: c-dynamic-dylib
----- /storage/home/achin/devel/rust/src/test/run-make/c-dynamic-dylib/ --------------------
------ stdout ---------------------------------------------
make[1]: Entering directory `/storage/home/achin/devel/rust/src/test/run-make/c-dynamic-dylib'
gcc -Wall -Werror -g -fPIC -m64 -L /storage/home/achin/devel/rust/x86_64-unknown-linux-gnu/test/run-make/c-dynamic-dylib -c -o /storage/home/achin/devel/rust/x86_64-unknown-linux-gnu/test/run-make/c-dynamic-dylib/libcfoo.o cfoo.c
gcc -Wall -Werror -g -fPIC -m64 -L /storage/home/achin/devel/rust/x86_64-unknown-linux-gnu/test/run-make/c-dynamic-dylib -o /storage/home/achin/devel/rust/x86_64-unknown-linux-gnu/test/run-make/c-dynamic-dylib/libcfoo.so /storage/home/achin/devel/rust/x86_64-unknown-linux-gnu/test/run-make/c-dynamic-dylib/libcfoo.o -shared
/storage/home/achin/devel/rust/x86_64-unknown-linux-gnu/stage2/bin/rustc --out-dir /storage/home/achin/devel/rust/x86_64-unknown-linux-gnu/test/run-make/c-dynamic-dylib -L /storage/home/achin/devel/rust/x86_64-unknown-linux-gnu/test/run-make/c-dynamic-dylib foo.rs
/storage/home/achin/devel/rust/x86_64-unknown-linux-gnu/stage2/bin/rustc --out-dir /storage/home/achin/devel/rust/x86_64-unknown-linux-gnu/test/run-make/c-dynamic-dylib -L /storage/home/achin/devel/rust/x86_64-unknown-linux-gnu/test/run-make/c-dynamic-dylib bar.rs
/storage/home/achin/devel/rust/x86_64-unknown-linux-gnu/test/run-make/c-dynamic-dylib/bar
rm /storage/home/achin/devel/rust/x86_64-unknown-linux-gnu/test/run-make/c-dynamic-dylib/libcfoo.o
make[1]: Leaving directory `/storage/home/achin/devel/rust/src/test/run-make/c-dynamic-dylib'

------ stderr ---------------------------------------------
/storage/home/achin/devel/rust/x86_64-unknown-linux-gnu/test/run-make/c-dynamic-dylib/bar: error while loading shared libraries: libcfoo.so: cannot open shared object file: No such file or directory
make[1]: *** [all] Error 127

------        ---------------------------------------------

```

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