enable compiler warnings for FFmpeg

None of the other external libraries have the warnings disabled.

In addition, the MythTV modifications no longer generate any additional warnings.

cmake/embeddedlibs/FindOrBuildFFmpeg.cmake

@@ -52,7 +52,7 @@ function(find_or_build_ffmpeg)
     --disable-stripping
     --disable-static
     --enable-shared
-    --extra-cflags=-w)
+    )
 
   if(NOT LIBS_INSTALL_PREFIX STREQUAL CMAKE_INSTALL_PREFIX)
     list(APPEND FF_ARGS --extra-cflags=-I${LIBS_INSTALL_PREFIX}/include

mythtv/configure

@@ -6798,7 +6798,6 @@ if enabled lto; then
     ffopts="$ffopts --enable-lto"
 fi
 
-ffmpeg_extra_cflags="$extra_cflags -w"
 if test "$ID" = "raspbian"; then
     case $cpu in
         armv*) ffmpeg_extra_ldflags="$ffmpeg_extra_libs -latomic" ;;