hg: build-infra/jdk8: Once again, restore the JOBS=n solution instead of -jN, which did not work

[magnus.ihse.bursie at oracle.com]

Changeset: 3aa4cd6cd76f
Author:    ihse
Date:      2012-06-11 14:35 +0200
URL:       http://hg.openjdk.java.net/build-infra/jdk8/rev/3aa4cd6cd76f

Once again, restore the JOBS=n solution instead of -jN, which did not work
properly for -j1 (arguably the most important case).

! common/makefiles/MakeBase.gmk
! common/makefiles/MakeHelpers.gmk
! common/makefiles/Makefile