Regression from 4563a86f.
Both need stdint.h included before the respective x264.h and xavs.h.

Old require() used different, separate checks that didn't actually
need stdint.h to work. require2()'s (now require) check_func_headers()
does include stdint.h but only after the custom headers.

For libxavs this would also be consequently fixed by libav's
commit 20abcaa2 which wasn't merged yet.