[Win32] Overload ==, != for locale_t and long long
_is_chartype_l (needed for isxdigit_l) in MinGW compares locale_t and NULL.
NULL is 'long long' for 64-bit, and this results in ambiguous overloads when
compiled with Clang. Define a concrete overload for the operators to fix the
Reviewers: mstorsjo, EricWF, srhines, danalbert
Subscribers: christof, cfe-commits, ldionne
Differential Revision: https://reviews.llvm.org/D48749