Auto merge of #26381 - alexcrichton:fix-srel, r=brson
Auto merge of #26381 - alexcrichton:fix-srel, r=brson

In #26252 support was added to have prettier paths printed out on failure by not
passing the full path to the source file to the compiler, but instead just a
small relative path. To preserve this relative path across configurations, the
`SREL` variable was used for reconfiguring, but if `SREL` is empty then it will
attempt to run the command `configure` which is distinct from running
`./configure` (e.g. doesn't run the local script).

This commit modifies the `SREL` value to re-run the configure script by setting
it to `./` in the case where `SREL` is empty.

nwin/rust,jroesch/rust,graydon/rust,jroesch/rust,KokaKiwi/rust,reem/rust,pelmers/rust,GBGamer/rust,jashank/rust,jashank/rust,reem/rust,aidancully/rust,reem/rust,vhbit/rust,nwin/rust,l0kod/rust,GBGamer/rust,aidancully/rust,graydon/rust,aidancully/rust,zubron/rust,pelmers/rust,nwin/rust,vhbit/rust,jroesch/rust,vhbit/rust,dwillmer/rust,KokaKiwi/rust,nwin/rust,reem/rust,KokaKiwi/rust,GBGamer/rust,jashank/rust,mvdnes/rust,pelmers/rust,zubron/rust,vhbit/rust,pelmers/rust,zubron/rust,l0kod/rust,jashank/rust,aidancully/rust,pshc/rust,graydon/rust,KokaKiwi/rust,zubron/rust,nwin/rust,pshc/rust,jashank/rust,pshc/rust,dwillmer/rust,omasanori/rust,graydon/rust,pshc/rust,graydon/rust,dwillmer/rust,jashank/rust,mvdnes/rust,graydon/rust,vhbit/rust,pshc/rust,nwin/rust,omasanori/rust,mvdnes/rust,pshc/rust,omasanori/rust,dwillmer/rust,jroesch/rust,nwin/rust,zubron/rust,zubron/rust,jroesch/rust,jroesch/rust,KokaKiwi/rust,nwin/rust,GBGamer/rust,l0kod/rust,zubron/rust,l0kod/rust,l0kod/rust,l0kod/rust,pelmers/rust,omasanori/rust,mvdnes/rust,dwillmer/rust,GBGamer/rust,vhbit/rust,mvdnes/rust,dwillmer/rust,l0kod/rust,dwillmer/rust,GBGamer/rust,zubron/rust,reem/rust,pelmers/rust,vhbit/rust,jroesch/rust,aidancully/rust,l0kod/rust,vhbit/rust,jroesch/rust,aidancully/rust,pshc/rust,omasanori/rust,GBGamer/rust,mvdnes/rust,reem/rust,dwillmer/rust,KokaKiwi/rust,GBGamer/rust,jashank/rust,omasanori/rust,pshc/rust,jashank/rust