ffmpeg: add option to build without GPL (#18909)

Author: techdragon

Formula/ffmpeg.rb

@@ -57,6 +57,7 @@ class Ffmpeg < Formula
   option "without-securetransport", "Disable use of SecureTransport"
   option "without-x264", "Disable H.264 encoder"
   option "without-xvid", "Disable Xvid MPEG-4 video encoder"
+  option "without-gpl", "Disable building GPL licensed parts of FFmpeg"
 
   deprecated_option "with-ffplay" => "with-sdl2"
   deprecated_option "with-sdl" => "with-sdl2"
@@ -111,7 +112,6 @@ def install
       --prefix=#{prefix}
       --enable-shared
       --enable-pthreads
-      --enable-gpl
       --enable-version3
       --enable-hardcoded-tables
       --enable-avresample
@@ -120,6 +120,7 @@ def install
       --host-ldflags=#{ENV.ldflags}
     ]
 
+    args << "--enable-gpl" if build.with? "gpl"
     args << "--disable-indev=qtkit" if build.without? "qtkit"
     args << "--disable-securetransport" if build.without? "securetransport"
     args << "--enable-chromaprint" if build.with? "chromaprint"