Can't use TerminateProcess with msys2 on Win7

Question

I'm making in gtk3 app that behaves like a launcher. I'm developing in linux and windows7 with msys2 and msvc2010. Everyhing is fine except that I can't use TerminateProcess because I get this warning:

implicit declaration of function 'TerminateProcess'

This is part of the code:

#if defined(G_OS_WIN32)
#if defined(__GNUC__)
#include <w32api.h>
#define WINVER WindowsXP
#define _WIN32_WINNT WindowsXP
#define _WIN32_WINDOWS WindowsXP
#define _WIN32_IE IE7
#endif
#include <processthreadsapi.h>
#endif
#include <gtk/gtk.h>

// ...

void kill_process (GPid pid)
{
#if defined(G_OS_WIN32)
    TerminateProcess (pid, 0);
#else
    kill (pid, SIGTERM);
#endif
    g_spawn_close_pid (pid);
}

The above function kill_process works as expected in linux and in windows (msvc 2010), but it doesn't with msys2 mingw64... any ideas?