Rollup merge of #24514 - krzysz00:no-warnings-in-liballoc, r=alexcrichton
Rollup merge of #24514 - krzysz00:no-warnings-in-liballoc, r=alexcrichton

When `liballoc` is compiled with `--cfg feature=\"external_features\"`, several `improper_ctypes` warnings are generated. Since these warnings are harmless, I have added a directive to suppress them.

TheNeikos/rust,gifnksm/rust,mihneadb/rust,andars/rust,pshc/rust,pshc/rust,graydon/rust,pelmers/rust,XMPPwocky/rust,omasanori/rust,dwillmer/rust,nwin/rust,XMPPwocky/rust,reem/rust,GBGamer/rust,nwin/rust,philyoon/rust,pshc/rust,victorvde/rust,graydon/rust,pelmers/rust,robertg/rust,ejjeong/rust,nwin/rust,vhbit/rust,TheNeikos/rust,aepsil0n/rust,pshc/rust,mihneadb/rust,jashank/rust,l0kod/rust,nwin/rust,ejjeong/rust,omasanori/rust,aneeshusa/rust,TheNeikos/rust,kwantam/rust,TheNeikos/rust,mvdnes/rust,KokaKiwi/rust,zachwick/rust,aidancully/rust,dwillmer/rust,reem/rust,aidancully/rust,aepsil0n/rust,carols10cents/rust,zubron/rust,jroesch/rust,mdinger/rust,zachwick/rust,rohitjoshi/rust,mvdnes/rust,victorvde/rust,GBGamer/rust,rohitjoshi/rust,aidancully/rust,reem/rust,omasanori/rust,KokaKiwi/rust,philyoon/rust,l0kod/rust,aneeshusa/rust,gifnksm/rust,andars/rust,mihneadb/rust,seanrivera/rust,mdinger/rust,zubron/rust,mvdnes/rust,victorvde/rust,dwillmer/rust,vhbit/rust,pshc/rust,aepsil0n/rust,aneeshusa/rust,mihneadb/rust,jashank/rust,carols10cents/rust,l0kod/rust,rohitjoshi/rust,TheNeikos/rust,dwillmer/rust,krzysz00/rust,vhbit/rust,nwin/rust,robertg/rust,ejjeong/rust,rohitjoshi/rust,zubron/rust,mihneadb/rust,mdinger/rust,GBGamer/rust,aepsil0n/rust,jashank/rust,pelmers/rust,philyoon/rust,victorvde/rust,l0kod/rust,seanrivera/rust,omasanori/rust,kwantam/rust,l0kod/rust,sae-bom/rust,KokaKiwi/rust,dwillmer/rust,ejjeong/rust,cllns/rust,jroesch/rust,jroesch/rust,reem/rust,zubron/rust,pshc/rust,robertg/rust,carols10cents/rust,nwin/rust,cllns/rust,omasanori/rust,robertg/rust,reem/rust,seanrivera/rust,GBGamer/rust,KokaKiwi/rust,zachwick/rust,kwantam/rust,graydon/rust,aneeshusa/rust,jashank/rust,cllns/rust,GBGamer/rust,mihneadb/rust,cllns/rust,pelmers/rust,dwillmer/rust,rohitjoshi/rust,victorvde/rust,reem/rust,zubron/rust,rohitjoshi/rust,mdinger/rust,gifnksm/rust,carols10cents/rust,XMPPwocky/rust,l0kod/rust,XMPPwocky/rust,l0kod/rust,vhbit/rust,aidancully/rust,aidancully/rust,sae-bom/rust,GBGamer/rust,aneeshusa/rust,TheNeikos/rust,krzysz00/rust,graydon/rust,zachwick/rust,mdinger/rust,sae-bom/rust,zubron/rust,sae-bom/rust,gifnksm/rust,dwillmer/rust,zubron/rust,KokaKiwi/rust,aneeshusa/rust,aidancully/rust,vhbit/rust,mvdnes/rust,jroesch/rust,nwin/rust,kwantam/rust,zachwick/rust,sae-bom/rust,jroesch/rust,pshc/rust,vhbit/rust,mdinger/rust,kwantam/rust,krzysz00/rust,l0kod/rust,graydon/rust,XMPPwocky/rust,jashank/rust,krzysz00/rust,andars/rust,aepsil0n/rust,jroesch/rust,vhbit/rust,ejjeong/rust,pelmers/rust,pelmers/rust,nwin/rust,omasanori/rust,cllns/rust,cllns/rust,philyoon/rust,andars/rust,carols10cents/rust,zachwick/rust,krzysz00/rust,seanrivera/rust,graydon/rust,vhbit/rust,kwantam/rust,GBGamer/rust,seanrivera/rust,victorvde/rust,dwillmer/rust,krzysz00/rust,carols10cents/rust,jroesch/rust,sae-bom/rust,andars/rust,robertg/rust,philyoon/rust,aepsil0n/rust,pshc/rust,ejjeong/rust,zubron/rust,XMPPwocky/rust,gifnksm/rust,philyoon/rust,robertg/rust,seanrivera/rust,GBGamer/rust,jroesch/rust,jashank/rust,gifnksm/rust,mvdnes/rust,KokaKiwi/rust,mvdnes/rust,andars/rust,jashank/rust,jashank/rust