src: ensure O_CLOEXEC is defined on Windows

Windows uses _O_NOINHERIT as the name for its O_CLOEXEC
equivalent. Define O_CLOEXEC to match this to fix
portability when we remove GNULIB.
Reviewed-by: NPavel Hrdina <phrdina@redhat.com>
Signed-off-by: NDaniel P. Berrangé <berrange@redhat.com>

src/internal.h

@@ -89,6 +89,12 @@
 
 #define NUL_TERMINATE(buf) do { (buf)[sizeof(buf)-1] = '\0'; } while (0)
 
+#ifdef WIN32
+# ifndef O_CLOEXEC
+#  define O_CLOEXEC _O_NOINHERIT
+# endif
+#endif
+
 /**
  * G_GNUC_NO_INLINE:
  *