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

contrib/llvm-project/clang/lib/CodeGen/CGVTables.cpp

@@ -437,7 +437,8 @@ void CodeGenFunction::EmitMustTailThunk(GlobalDecl GD,
   // Finish the function to maintain CodeGenFunction invariants.
   // FIXME: Don't emit unreachable code.
   EmitBlock(createBasicBlock());
-  FinishFunction();
+
+  FinishThunk();
 }
 
 void CodeGenFunction::generateThunk(llvm::Function *Fn,
@@ -564,7 +565,7 @@ llvm::Constant *CodeGenVTables::maybeEmitThunk(GlobalDecl GD,
   CGM.SetLLVMFunctionAttributesForDefinition(GD.getDecl(), ThunkFn);
 
   // Thunks for variadic methods are special because in general variadic
-  // arguments cannot be perferctly forwarded. In the general case, clang
+  // arguments cannot be perfectly forwarded. In the general case, clang
   // implements such thunks by cloning the original function body. However, for
   // thunks with no return adjustment on targets that support musttail, we can
   // use musttail to perfectly forward the variadic arguments.