Makefile: setup-config and setup-git got right
Makefile: including tweaks for build improvements

mk/tweaks.mk: JOBS variable for parallelizing the make recursion
mk/tweaks.mk: LLVM_SUBMOD for adding a dependency to the default rule
FIX: removed useless rule dependency
FIX: avoid the src-all dependencies chime into -install -clean
FIX: job number shell calculation to proper call function