add libwebp support

scripts/parse-arguments.sh

@@ -22,6 +22,7 @@ SUPPORTED_LIBRARIES_FREE=(
   "libtwolame"
   "libspeex"
   "libvpx"
+  "libwebp"
   "libfreetype"
   "libfribidi"
 )
@@ -85,6 +86,9 @@ for argument in "$@"; do
   --enable-libopus | -opus)
     EXTERNAL_LIBRARIES+=("libopus")
     ;;
+  --enable-webp | -webp)
+    EXTERNAL_LIBRARIES+=("libwep")
+    ;;
   --enable-libwavpack | -wavpack)
     EXTERNAL_LIBRARIES+=("libwavpack")
     ;;