Changed use -jX here for parallelism to use "-j N" for N parallel jobs
Rationale: In my opinion use -jX here for parallelism is quite ambiguous as it could be perceived as a single option without any argument. Ie running:
0make -jX
Embarrassingly this caused me to be stuck for quite a long time until I opened the help menu for make but if I am the only one who faced this issue I would be happy to close this PR.