Include <stdint.h> in glib/valgrind.h

This ensures the uintptr_t type is defined on mingw-w64.

Fixes compile error:

make[4]: Entering directory
`/home/abuild/rpmbuild/BUILD/glib-2.42.0/gobject'
  CC       libgobject_2_0_la-gtype.lo
In file included from gtype.c:24:0:
../glib/valgrind.h: In function 'VALGRIND_PRINTF':
../glib/valgrind.h:5601:4: error: unknown type name 'uintptr_t'
    uintptr_t _qzz_res;
    ^

https://bugzilla.gnome.org/show_bug.cgi?id=737143