Index: setup/parallel_build.py
--- setup/parallel_build.py.orig
+++ setup/parallel_build.py
@@ -22,6 +22,8 @@ Job = namedtuple('Job', 'cmd human_text cwd')
 
 cpu_count = min(16, max(1, os.cpu_count()))
 
+# let MAKE_JOBS override how many cpus are used
+cpu_count = min(cpu_count, int(os.environ.get('MAKE_JOBS', 1)))
 
 def run_worker(job, decorate=True):
     cmd, human_text = job.cmd, job.human_text
