Add support for __wchar_t in -fms-extensions mode.

MSVC provides __wchar_t. This is the same as the built-in wchar_t type
from C++, but it is also available with -fno-wchar and in C.

The commit changes ASTContext to have two different types for this:

  - WCharTy is the built-in type used for wchar_t in C++ and __wchar_t.

  - WideCharTy is the type of a wide character literal. In C++ this is
    the same as WCharTy, and in C  it is an integer type compatible with
    the type in <stddef.h>.

This fixes PR15815.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@181587 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Sema/SemaInit.cpp b/lib/Sema/SemaInit.cpp
index 9e8936e..7016e56 100644
--- a/lib/Sema/SemaInit.cpp
+++ b/lib/Sema/SemaInit.cpp
@@ -65,7 +65,7 @@
     // correction from DR343): "An array with element type compatible with a
     // qualified or unqualified version of wchar_t may be initialized by a wide
     // string literal, optionally enclosed in braces."
-    if (Context.typesAreCompatible(Context.getWCharType(),
+    if (Context.typesAreCompatible(Context.getWideCharType(),
                                    ElemTy.getUnqualifiedType()))
       return Init;