As discussed on the mailing list in "Clang on Windows fails to detect trivial double free in static analysis", the "unix" checkers are also applicable on Windows, and enables Malloc/MallocSizeof/cstring.BadSizeArg/cstring.NullArg/API checking. This patch enables the unix checkers by removing the "IsWindowsMSVC" check.
(I haven't actually compiled this yet, but will do so immediately)