SlideSignal media runtime reproducible build recipe

Target: macOS arm64, minimum deployment target 14.0.
Jobs: make -j4.

Sources
-------
FFmpeg: 9.0.2, source/ffmpeg-9.0.2.tar.xz
x264: stable revision b35605ace3ddf7c1a5d67a2eb553f034aef41d55,
source/x264-b35605ace3ddf7c1a5d67a2eb553f034aef41d55.tar.gz

Build x264 from its extracted source directory:
  MACOSX_DEPLOYMENT_TARGET=14.0 CFLAGS='-mmacosx-version-min=14.0' \
  LDFLAGS='-mmacosx-version-min=14.0' ./configure \
  --prefix=$X264_PREFIX --enable-static --disable-cli --enable-pic
  MACOSX_DEPLOYMENT_TARGET=14.0 make -j4
  make install

Build FFmpeg from its extracted source directory. Set X264_PREFIX to the
x264 installation above and use a separate FFmpeg prefix:
  MACOSX_DEPLOYMENT_TARGET=14.0 PKG_CONFIG_PATH= \
  PKG_CONFIG_LIBDIR=$X264_PREFIX/lib/pkgconfig \
  CFLAGS="-mmacosx-version-min=14.0 -I$X264_PREFIX/include" \
  LDFLAGS="-mmacosx-version-min=14.0 -L$X264_PREFIX/lib" \
  ./configure --prefix=$FFMPEG_PREFIX --pkg-config-flags=--static \
  --extra-cflags="-mmacosx-version-min=14.0 -I$X264_PREFIX/include" \
  --extra-ldflags="-mmacosx-version-min=14.0 -L$X264_PREFIX/lib" \
  --extra-libs='-lpthread -lm' --extra-version=slidesignal-media-runtime \
  --disable-autodetect --enable-gpl --enable-libx264 \
  --enable-videotoolbox --enable-audiotoolbox --enable-zlib \
  --enable-pthreads --enable-static --disable-shared --disable-debug \
  --disable-doc
  MACOSX_DEPLOYMENT_TARGET=14.0 make -j4
  make install

The build intentionally uses no external libraries other than x264. The
system frameworks and zlib are supplied by macOS. Verify both outputs with
`file`, `otool -l` (LC_BUILD_VERSION minos 14.0), and `otool -L` before use.
