[mac] Restore an upper limit on the number of jobs on macOS

Even when increasing the maximum number of file descriptor
as recommended in the documentation, using a large number
of concurrent jobs cause build error on certain macOS devices
(mostly iMacPro with 18 cores which ends up with a limit of
1440 jobs, and end up reaching the heightened file descriptor
limit).

Put a limit of 800 which has been found to work on all of
the devices available and still allow to have a multiplier
of 80 on highest end M1 devices (currently 10 cores).

Bug: 1317620, 936864
Change-Id: I32560c5ae9462e94f61a773d625ef3758bf05ee5
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/3634807Reviewed-by: Takuto Ikuta <tikuta@chromium.org>
Auto-Submit: Sylvain Defresne <sdefresne@chromium.org>
Commit-Queue: Jochen Eisinger <jochen@chromium.org>
Reviewed-by: Jochen Eisinger <jochen@chromium.org>

autoninja.py

@@ -185,6 +185,10 @@ def main(args):
         # On windows, j value higher than 1000 does not improve build
         # performance.
         j_value = min(j_value, 1000)
+      elif sys.platform == 'darwin':
+        # On macOS, j value higher than 800 causes 'Too many open files' error
+        # (crbug.com/936864).
+        j_value = min(j_value, 800)
 
       args.append('%d' % j_value)
     else: