CodeGenModule: Always output wchar_size, check LLVM assumptions.
Re-commit r303463 now that LLVM is fixed and adjust some lit tests.
llvm::TargetLibraryInfo needs to know the size of wchar_t to work on
functions like `wcslen`. This patch changes clang to always emit the
wchar_size module flag (it would only do so for ARM previously).
This also adds an `assert()` to ensure the LLVM defaults based on the
target triple are in sync with clang.
Differential Revision: https://reviews.llvm.org/D32982
git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@303478
91177308-0d34-0410-b5e6-
96231b3b80d8