Revert: "Re: [lld] r249752 - Revert: r249728 - Roll back r249726 and r249723...

Revert: "Re: [lld] r249752 - Revert: r249728 - Roll back r249726 and r249723 because they broke buildbots."

This has turned out to be unnecessary, and while some ability to set VAStart
will be needed at some point, this is not clearly the right direction.

llvm-svn: 250205