[gm.py] Fix goma process detection on MacOS

On MacOS, `ps -e | grep foo` always finds a match, because `ps`
already sees the `grep` command, which matches the search string.
Luckily, `pgrep` exists as an elegant alternative.

No-Try: true
Change-Id: Ieedfe62ab11a59fb9a29ae1ebd39b164eec5193c
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3144917
Auto-Submit: Jakob Kummerow <jkummerow@chromium.org>
Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Commit-Queue: Jakob Kummerow <jkummerow@chromium.org>
Cr-Commit-Position: refs/heads/main@{#76707}

tools/dev/gm.py

@@ -506,7 +506,7 @@ def Main(argv):
   return_code = 0
   # If we have Goma but it is not running, start it.
   if (IS_GOMA_MACHINE and
-      _Call("ps -e | grep compiler_proxy > /dev/null", silent=True) != 0):
+      _Call("pgrep -x compiler_proxy > /dev/null", silent=True) != 0):
     _Call("%s/goma_ctl.py ensure_start" % GOMADIR)
   for c in configs:
     return_code += configs[c].Build()