Add workaround for unstable gn on macOS in ci

In ci 'gn' can crash making it hard to integrate, if there
is high load crashes occur more frequently sometimes even
blocking integrations for few days.

Limit number of worker threads for gn as this improves situation
however increases time for generating ninja files from 2s to 7s.

Note this will not prevent crashes however significantly reduces the
issue (when running in loop from 1 per ~10min to 1 per ~3days)

Compilation with address or thread sanitizer does not lead to meaningful
traces. Moreover running gn with sanitizer creates deadlocks for
unknown reason every few runs.

Current assumptions is that macos vms are unstable as crashes also occur
for sscache calls (compiler) and python calls.

Change-Id: I1c488796eb0547eedd20101606f18ed55718e9c2
Reviewed-by: Alexandru Croitor <alexandru.croitor@qt.io>
(cherry picked from commit 2c5b25387c89420cc04decb1298356e452bb5fe5)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>

0 files changed, 0 insertions, 0 deletions