misc: fix the MAKE_PARALLEL_JOBS for 'make verify' target

MAKE_PARALLEL_JOBS was prepending "-j", which in case of nested targets like "verify"
resulted in ninja being executed with "-j -j" flags.

Solution: prepend -j only at the moment of setting the MAKE_PARALLEL_FLAGS variable,
this keeps MAKE_PARALLEL_JOBS intact regardless of depth of the job call tree.

Type: make
Signed-off-by: Andrew Yourtchenko <ayourtch@gmail.com>
Change-Id: I10a69fe527758e5a862852a9f2102aeaca30e88f

build-root/Makefile

@@ -653,12 +653,10 @@ configure_check_timestamp =						\
 # NB: GNU Make 4.2 will let us use '$(file </proc/cpuinfo)' to both test
 # for file presence and content; for now this will have to do.
 ifndef MAKE_PARALLEL_JOBS
-MAKE_PARALLEL_JOBS = -j $(if $(shell [ -f /proc/cpuinfo ] && head /proc/cpuinfo), \
+MAKE_PARALLEL_JOBS = $(if $(shell [ -f /proc/cpuinfo ] && head /proc/cpuinfo), \
 	$(shell grep -c ^processor /proc/cpuinfo), 2)
-else
-MAKE_PARALLEL_JOBS := -j $(MAKE_PARALLEL_JOBS)
 endif
-MAKE_PARALLEL_FLAGS ?= $(if $($(PACKAGE)_make_parallel_fails),,$(MAKE_PARALLEL_JOBS))
+MAKE_PARALLEL_FLAGS ?= $(if $($(PACKAGE)_make_parallel_fails),,-j $(MAKE_PARALLEL_JOBS))
 
 # Make command shorthand for packages & tools.
 PACKAGE_MAKE =					\