I've found & fixed a leak that Clang misses when compiling on Windows.
The leak was found by SARD #149071, mem1-bad.c. Clang misses it because MSVC uses _strdup instead of strdup. I've added an IdentifierInfo* for _strdup, and now Clang catches it.
As a drive by fix, I added the wide character strdup variants (wcsdup, _wcsdup) and the MSVC version of alloca (_alloca).
No new check-all failures. (Did somebody improve lit's output?) Adding reviewers...