add back `noalias` to `&mut T` pointer parameters
add back `noalias` to `&mut T` pointer parameters

This was removed because these could alias with `&const T` or `@mut T`
and those are now gone from the language. There are still aliasing
issues within local scopes, but this is correct for function parameters.

This also removes the no-op `noalias` marker on proc (not a pointer) and
leaves out the mention of #6750 because real type-based alias analysis
is not within the scope of best effort usage of the `noalias` attribute.

Test case:

    pub fn foo(x: &mut &mut u32) {
        **x = 5;
        **x = 5;
    }

Before:

    define void @_ZN3foo20h0ce94c9671b0150bdaa4v0.0E(i32** nocapture readonly) unnamed_addr #0 {
    entry-block:
      %1 = load i32** %0, align 8
      store i32 5, i32* %1, align 4
      %2 = load i32** %0, align 8
      store i32 5, i32* %2, align 4
      ret void
    }

After:

    define void @_ZN3foo20h0ce94c9671b0150bdaa4v0.0E(i32** noalias nocapture readonly) unnamed_addr #0 {
    entry-block:
      %1 = load i32** %0, align 8
      store i32 5, i32* %1, align 4
      ret void
    }

Closes #12436

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