update: add CC environment option to mp-build

mp-build/scripts/mp-build.sh

@@ -344,6 +344,7 @@ done
 unset_indent
 
 info "Running the build function"
+export CC="gcc"
 export CFLAGS="-march=x86-64 -mtune=generic -O2"
 export ROOTDIR="${rootpath}"
 export MAKEFLAGS="-j${OPT_CORES}"
@@ -363,8 +364,8 @@ else
 fi
 
 unset XORG_CONFIG XORG_PREFIX
-unset CFLAGS ROOTDIR
 unset MAKEOPTS MAKEFLAGS
+unset CFLAGS ROOTDIR CC
 
 if [ "$SECONDS" != "0" ]; then
   success "Completed the build in ${SECONDS}s"