Inherit MAKEFLAGS from environment if defined

etc/astronaut.conf

@@ -25,6 +25,6 @@ package_options() {
 
 export CFLAGS='-mtune=atom -pipe -O3'
 export CXXFLAGS="$CFLAGS"
-export MAKEFLAGS="-j $(grep processor /proc/cpuinfo | wc -l)"
+export MAKEFLAGS="${MAKEFLAGS:--j $(grep processor /proc/cpuinfo | wc -l)}"
 export WAFFLAGS="$MAKEFLAGS"
 export BAMFLAGS="$MAKEFLAGS"