configure: #include stdint.h as part of libxavs test

Unfortunately the xavs.h API header is not self-sufficient and relies
on manual stdint.h inclusion by its users.

configure

@@ -4673,7 +4673,7 @@ enabled libx264           && require_pkg_config x264 "stdint.h x264.h" x264_enco
 enabled libx265           && require_pkg_config x265 x265.h x265_api_get &&
                              { check_cpp_condition x265.h "X265_BUILD >= 57" ||
                                die "ERROR: libx265 version must be >= 57."; }
-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 mmal              && { check_lib interface/mmal/mmal.h mmal_port_connect -lmmal_core -lmmal_util -lmmal_vc_client -lbcm_host ||
                                 { ! enabled cross_compile && {