Rollup merge of #23004 - alexcrichton:libc-stable, r=brson
Rollup merge of #23004 - alexcrichton:libc-stable, r=brson

 This same source is being built in the Cargo ecosystem and hence needs to build
on stable Rust as well. This commit places the `no_std` attribute along with the
`no_std` feature behind a `cfg_attr` flag so they are not processed when
compiled on crates.io

mvdnes/rust,nwin/rust,pelmers/rust,GBGamer/rust,zubron/rust,l0kod/rust,rprichard/rust,vhbit/rust,rprichard/rust,pshc/rust,jashank/rust,krzysz00/rust,jashank/rust,seanrivera/rust,rprichard/rust,andars/rust,pelmers/rust,krzysz00/rust,rohitjoshi/rust,l0kod/rust,zachwick/rust,gifnksm/rust,nwin/rust,philyoon/rust,rohitjoshi/rust,kwantam/rust,KokaKiwi/rust,omasanori/rust,AerialX/rust,krzysz00/rust,jroesch/rust,ejjeong/rust,jroesch/rust,mahkoh/rust,aidancully/rust,reem/rust,AerialX/rust,zachwick/rust,l0kod/rust,GBGamer/rust,l0kod/rust,carols10cents/rust,sae-bom/rust,zubron/rust,zubron/rust,graydon/rust,cllns/rust,miniupnp/rust,miniupnp/rust,TheNeikos/rust,dwillmer/rust,ejjeong/rust,rprichard/rust,jroesch/rust,gifnksm/rust,philyoon/rust,jashank/rust,aneeshusa/rust,ebfull/rust,krzysz00/rust,seanrivera/rust,zaeleus/rust,AerialX/rust-rt-minimal,aneeshusa/rust,jashank/rust,ebfull/rust,ruud-v-a/rust,avdi/rust,omasanori/rust,vhbit/rust,pshc/rust,mahkoh/rust,avdi/rust,aidancully/rust,omasanori/rust,AerialX/rust-rt-minimal,mdinger/rust,cllns/rust,mihneadb/rust,victorvde/rust,zubron/rust,andars/rust,robertg/rust,pshc/rust,andars/rust,jashank/rust,mvdnes/rust,zachwick/rust,mvdnes/rust,AerialX/rust-rt-minimal,andars/rust,sae-bom/rust,jroesch/rust,mvdnes/rust,dwillmer/rust,zubron/rust,mahkoh/rust,aneeshusa/rust,miniupnp/rust,pelmers/rust,victorvde/rust,robertg/rust,jashank/rust,XMPPwocky/rust,vhbit/rust,pshc/rust,mihneadb/rust,nwin/rust,robertg/rust,mdinger/rust,AerialX/rust,KokaKiwi/rust,carols10cents/rust,AerialX/rust-rt-minimal,philyoon/rust,mihneadb/rust,aidancully/rust,omasanori/rust,vhbit/rust,ruud-v-a/rust,ejjeong/rust,nwin/rust,zubron/rust,dwillmer/rust,AerialX/rust,robertg/rust,KokaKiwi/rust,ruud-v-a/rust,rohitjoshi/rust,reem/rust,TheNeikos/rust,pshc/rust,aidancully/rust,reem/rust,vhbit/rust,rohitjoshi/rust,XMPPwocky/rust,miniupnp/rust,cllns/rust,TheNeikos/rust,victorvde/rust,cllns/rust,mdinger/rust,GBGamer/rust,aepsil0n/rust,aepsil0n/rust,kwantam/rust,jroesch/rust,jroesch/rust,reem/rust,mihneadb/rust,mvdnes/rust,KokaKiwi/rust,zaeleus/rust,miniupnp/rust,seanrivera/rust,dwillmer/rust,KokaKiwi/rust,avdi/rust,gifnksm/rust,XMPPwocky/rust,AerialX/rust,robertg/rust,victorvde/rust,XMPPwocky/rust,rprichard/rust,pshc/rust,seanrivera/rust,zachwick/rust,omasanori/rust,rohitjoshi/rust,pelmers/rust,graydon/rust,sae-bom/rust,l0kod/rust,XMPPwocky/rust,AerialX/rust-rt-minimal,zachwick/rust,robertg/rust,dwillmer/rust,ejjeong/rust,nwin/rust,aidancully/rust,zaeleus/rust,ebfull/rust,miniupnp/rust,GBGamer/rust,aepsil0n/rust,miniupnp/rust,nwin/rust,aepsil0n/rust,graydon/rust,l0kod/rust,kwantam/rust,dwillmer/rust,dwillmer/rust,zaeleus/rust,mdinger/rust,ruud-v-a/rust,zaeleus/rust,vhbit/rust,sae-bom/rust,TheNeikos/rust,ebfull/rust,TheNeikos/rust,GBGamer/rust,seanrivera/rust,jroesch/rust,TheNeikos/rust,pelmers/rust,pelmers/rust,avdi/rust,reem/rust,aneeshusa/rust,omasanori/rust,ruud-v-a/rust,avdi/rust,graydon/rust,aneeshusa/rust,carols10cents/rust,jashank/rust,miniupnp/rust,philyoon/rust,ebfull/rust,zaeleus/rust,aepsil0n/rust,graydon/rust,graydon/rust,aneeshusa/rust,mdinger/rust,mdinger/rust,carols10cents/rust,l0kod/rust,krzysz00/rust,rprichard/rust,pshc/rust,carols10cents/rust,mihneadb/rust,mvdnes/rust,jroesch/rust,aidancully/rust,kwantam/rust,mihneadb/rust,vhbit/rust,mahkoh/rust,victorvde/rust,krzysz00/rust,mahkoh/rust,dwillmer/rust,kwantam/rust,andars/rust,rohitjoshi/rust,mahkoh/rust,zubron/rust,avdi/rust,pshc/rust,AerialX/rust,ejjeong/rust,AerialX/rust-rt-minimal,gifnksm/rust,cllns/rust,carols10cents/rust,XMPPwocky/rust,andars/rust,zachwick/rust,nwin/rust,ebfull/rust,philyoon/rust,zubron/rust,gifnksm/rust,cllns/rust,aepsil0n/rust,philyoon/rust,GBGamer/rust,l0kod/rust,sae-bom/rust,jashank/rust,ejjeong/rust,kwantam/rust,sae-bom/rust,reem/rust,KokaKiwi/rust,nwin/rust,vhbit/rust,seanrivera/rust,victorvde/rust,GBGamer/rust,gifnksm/rust,ruud-v-a/rust,GBGamer/rust