valgrind.h is a verbatim copy taken from Valgrind project. Previously
that file had local changes that got dropped by last update. To avoid
regressing again, do not edit valgrind.h anymore and instead add a
gvalgrind.h wrapper that gets included instead.

This fix 2 errors:
- uintptr_t is not defined when including valgrind.h on mingw.
- MSVC compiler is not supported on amd64-Win64 platform.