Add a basic script to show how to build macOS with aom+rav1e+dav1d

scripts/build_macos.sh

@@ -0,0 +1,43 @@
+#!/bin/bash
+
+if ! [ -x "$(command -v meson)" ]; then
+  echo 'Error: meson is not installed.' >&2
+  exit 1
+fi
+if ! [ -x "$(command -v cargo)" ]; then
+  echo 'Error: cargo (Rust) is not installed.' >&2
+  exit 1
+fi
+if ! [ -x "$(command -v nasm)" ]; then
+  echo 'Error: nasm is not installed.' >&2
+  exit 1
+fi
+if ! [ -x "$(command -v ninja)" ]; then
+  echo 'Error: ninja is not installed.' >&2
+  exit 1
+fi
+if ! [ -x "$(command -v cmake)" ]; then
+  echo 'Error: cmake is not installed.' >&2
+  exit 1
+fi
+if ! [ -x "$(command -v git)" ]; then
+  echo 'Error: git is not installed.' >&2
+  exit 1
+fi
+
+DIR="$( cd "$( dirname "${BASH_SOURCE[0]}" )" >/dev/null 2>&1 && pwd )"
+cd "$DIR/.."
+COLORIST_ROOT=`pwd`
+echo Colorist Root: $COLORIST_ROOT 
+
+cd ext/avif/ext
+$SHELL ./dav1d.cmd
+$SHELL ./rav1e.cmd
+cd ../../..
+mkdir build
+cd build
+cmake -G Ninja -DAVIF_CODEC_DAV1D=1 -DAVIF_LOCAL_DAV1D=1 -DAVIF_CODEC_RAV1E=1 -DAVIF_LOCAL_RAV1E=1 -DCMAKE_BUILD_TYPE=Release ..
+ninja
+
+echo If there are no errors above, "$COLORIST_ROOT/build/bin/colorist/colorist" should be available. Copy/link it somewhere in your PATH.
+