libmfx install
autoreconf -i
./configure --prefix=$HOME/ffmpeg_build
make -j 18
make install

PKG_CONFIG_PATH="$HOME/ffmpeg_build/lib/pkgconfig" ./configure --prefix="$HOME/ffmpeg_build" --extra-cflags="-I$HOME/ffmpeg_build/include" --extra-ldflags="-L$HOME/ffmpeg_build/lib" --bindir="$HOME/bin" --pkg-config-flags="" --enable-gpl --enable-nonfree --enable-libfdk-aac --enable-libmp3lame --enable-libopus --enable-libvorbis --enable-libvpx --enable-libx264 --enable-libmfx

tail config.log
    3   int main(void) { return 0; }
END /tmp/ffconf.srZzUVvD.c
gcc -D_ISOC99_SOURCE -D_FILE_OFFSET_BITS=64 -D_LARGEFILE_SOURCE -D_POSIX_C_SOURCE=200112 -D_XOPEN_SOURCE=600 -I/home/brian/ffmpeg_build/include -std=c99 -fomit-frame-pointer -pthread -I/home/brian/ffmpeg_build/include -I/home/brian/ffmpeg_build/include -L/home/brian/ffmpeg_build/lib -c -o /tmp/ffconf.T8XBOPjH.o /tmp/ffconf.srZzUVvD.c
gcc -L/home/brian/ffmpeg_build/lib -Wl,--as-needed -Wl,-z,noexecstack -I/home/brian/ffmpeg_build/include -L/home/brian/ffmpeg_build/lib -o /tmp/ffconf.knjn9Kq7 /tmp/ffconf.T8XBOPjH.o -lmfx -lstdc++ -ldl -L/home/brian/ffmpeg_build/lib -lfdk-aac -lm -lm -lz -pthread
/home/brian/ffmpeg_build/lib/libmfx.a(libmfx_la-main.o): In function `init_internal_hwctx':
/home/brian/mfx_dispatch/src/main.cpp:930: undefined reference to `mfx_allocate_va'
/home/brian/ffmpeg_build/lib/libmfx.a(libmfx_la-main.o): In function `MFXClose':
/home/brian/mfx_dispatch/src/main.cpp:531: undefined reference to `mfx_deallocate_va'
collect2: error: ld returned 1 exit status
ERROR: libmfx not found using pkg-config