Merge commit ce5173c0e from llvm git (by Reid Kleckner):

Merge commit ce5173c0e from llvm git (by Reid Kleckner):

  Use FinishThunk to finish musttail thunks

  FinishThunk, and the invariant of setting and then unsetting
  CurCodeDecl, was added in 7f416cc42638 (2015). The invariant didn't
  exist when I added this musttail codepath in ab2090d10765 (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

This should fix 'Assertion failed: (!empty() && "popping exception stack
when not empty"), function popTerminate, file
/usr/src/contrib/llvm-project/clang/lib/CodeGen/CGCleanup.h, line 583'
when building the net-p2p/libtorrent-rasterbar

PR:		244830
Reported by:	jbeich, yuri
MFC after:	6 weeks
X-MFC-With:	358851