In an effort to reduce the likelihood of text getting out of sync, reusing the text from some diagnostics explicitly. No functional changes intended.

git-svn-id: http://llvm.org/svn/llvm-project/cfe/trunk@198078 91177308-0d34-0410-b5e6-96231b3b80d8
[ms-cxxabi] Emit fewer trivial return adjusting thunks

Most importantly, this makes our vtable layout match MSVC's.  Previously
we would emit a return adjusting thunk whenever the return types
differed, even if the adjustment would have been trivial.

MSVC does emit some trivial return adjusting thunks, but only if there
was already an overridden method that required a return adjustment.

git-svn-id: http://llvm.org/svn/llvm-project/cfe/trunk@198080 91177308-0d34-0410-b5e6-96231b3b80d8
Fix incorrect copy-pasted method decl that MSVC allowed.

git-svn-id: http://llvm.org/svn/llvm-project/cfe/trunk@198081 91177308-0d34-0410-b5e6-96231b3b80d8
Implement MSVC header search algorithm in MicrosoftMode.
Follows algorithm described here: http://msdn.microsoft.com/en-us/library/36k2cdd4.aspx

git-svn-id: http://llvm.org/svn/llvm-project/cfe/trunk@198082 91177308-0d34-0410-b5e6-96231b3b80d8