configure: add stdint.h to x264 and xavs checks

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.

configure

@@ -5848,7 +5848,7 @@ enabled libwebp           && {
     enabled libwebp_encoder      && require_pkg_config "libwebp >= 0.2.0" webp/encode.h WebPGetEncoderVersion
     enabled libwebp_anim_encoder && { use_pkg_config "libwebpmux >= 0.4.0" webp/mux.h WebPAnimEncoderOptionsInit || disable libwebp_anim_encoder; } }
 enabled libx264           && { use_pkg_config x264 "stdint.h x264.h" x264_encoder_encode ||
-                               { require libx264 x264.h x264_encoder_encode -lx264 &&
+                               { require libx264 "stdint.h x264.h" x264_encoder_encode -lx264 &&
                                  warn "using libx264 without pkg-config"; } } &&
                              { check_cpp_condition x264.h "X264_BUILD >= 118" ||
                                die "ERROR: libx264 must be installed and version must be >= 0.118."; } &&
@@ -5857,7 +5857,7 @@ enabled libx264           && { use_pkg_config x264 "stdint.h x264.h" x264_encode
 enabled libx265           && require_pkg_config x265 x265.h x265_api_get &&
                              { check_cpp_condition x265.h "X265_BUILD >= 68" ||
                                die "ERROR: libx265 version must be >= 68."; }
-enabled libxavs           && require libxavs xavs.h xavs_encoder_encode -lxavs
+enabled libxavs           && require libxavs "stdint.h xavs.h" xavs_encoder_encode -lxavs
 enabled libxvid           && require libxvid xvid.h xvid_global -lxvidcore
 enabled libzimg           && require_pkg_config "zimg >= 2.3.0" zimg.h zimg_get_api_version
 enabled libzmq            && require_pkg_config libzmq zmq.h zmq_ctx_new