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/Analysis/ScanfFormatString.cpp b/lib/Analysis/ScanfFormatString.cpp
index 2dbc9e4..676b68f 100644
--- a/lib/Analysis/ScanfFormatString.cpp
+++ b/lib/Analysis/ScanfFormatString.cpp
@@ -311,7 +311,7 @@
         case LengthModifier::None:
           return ArgType::PtrTo(ArgType::AnyCharTy);
         case LengthModifier::AsLong:
-          return ArgType::PtrTo(ArgType(Ctx.getWCharType(), "wchar_t"));
+          return ArgType::PtrTo(ArgType(Ctx.getWideCharType(), "wchar_t"));
         case LengthModifier::AsAllocate:
         case LengthModifier::AsMAllocate:
           return ArgType::PtrTo(ArgType::CStrTy);
@@ -323,7 +323,7 @@
       // FIXME: Mac OS X specific?
       switch (LM.getKind()) {
         case LengthModifier::None:
-          return ArgType::PtrTo(ArgType(Ctx.getWCharType(), "wchar_t"));
+          return ArgType::PtrTo(ArgType(Ctx.getWideCharType(), "wchar_t"));
         case LengthModifier::AsAllocate:
         case LengthModifier::AsMAllocate:
           return ArgType::PtrTo(ArgType(ArgType::WCStrTy, "wchar_t *"));