Ports/SDL_sound: Ensure build is run in parallel

Author: https://github.com/tcl3
Commit: d09271be35
Pull-request: https://github.com/SerenityOS/serenity/pull/20710
Reviewed-by: https://github.com/timschumi ✅

Ports/SDL_sound/package.sh

@@ -19,6 +19,6 @@ configopts=(
     '--enable-speex=no'
     "--with-sdl-prefix=${SERENITY_INSTALL_ROOT}/usr/local"
 )
-makeopts=(
+makeopts+=(
     'LDFLAGS=-lm'
 )