Made the mechanism of defining preprocessor defs for maxint, ptrdiff_t, wchar

Made the mechanism of defining preprocessor defs for maxint, ptrdiff_t, wchar
etc more generic. For some targets, long may not be equal to pointer size. For
example: PIC16 has int as i16, ptr as i16 but long as i32.

Also fixed a few build warnings in assert() functions in CFRefCount.cpp,
CGDecl.cpp, SemaDeclCXX.cpp and ParseDeclCXX.cpp.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@58501 91177308-0d34-0410-b5e6-96231b3b80d8