I think byval/sret and the others are close to being able to rip out
the code to support the missing type case. A lot of this code is
shared with inalloca, so catch this up to the others so that can
happen.
FinishThunk, and the invariant of setting and then unsetting
CurCodeDecl, was added in 7f416cc426 (2015). The invariant didn't
exist when I added this musttail codepath in ab2090d107 (2014).
Recently in 28328c3771, I started using this codepath on non-Windows
platforms, and users reported problems during release testing (PR44987).
The issue was already present for users of EH on i686-windows-msvc, so I
added a test for that case as well.
Reviewed By: hans
Differential Revision: https://reviews.llvm.org/D76444
Matt Arsenault