Build GCC with 2 threads

Author: GuillaumeGomez

src/ci/docker/host-x86_64/dist-x86_64-linux/build-gccjit.sh

@@ -25,7 +25,7 @@ cd ../gcc-build
     --prefix=$(pwd)/../gcc-install \
     --quiet
 
-hide_output make
+hide_output make -j2
 hide_output make install
 
 rm -rf ../gcc-src