Pass through CXXFLAGS from parent environment

Currently this clobbers any existing CXXFLAGS when configuring x264, this will remove any user specified optimisation or hardening flags. Changing it to prepend to any potential existing CXXFLAG.

Author: barberio

build-ffmpeg

@@ -481,7 +481,7 @@ if $NONFREE_AND_GPL; then
     cd "${PACKAGES}"/x264-5db6aa6 || exit
 
     if [[ "$OSTYPE" == "linux-gnu" ]]; then
-      execute ./configure --prefix="${WORKSPACE}" --enable-static --enable-pic CXXFLAGS="-fPIC"
+      execute ./configure --prefix="${WORKSPACE}" --enable-static --enable-pic CXXFLAGS="-fPIC ${CXXFLAGS}"
     else
       execute ./configure --prefix="${WORKSPACE}" --enable-static --enable-pic
     fi