Use 2 cores per job in github build

As of today, https://docs.github.com/en/actions/reference/virtual-environments-for-github-hosted-runners
states that hosted runners have a 2-core CPU.

This uses make -j $physical_cores to try and be better about utilizing the time spent on those machines.
When github upgrades runners to have more cores we'll benefit from that too.

Author: kvc0

tools/build_release_files.py

@@ -5,6 +5,7 @@
 # SPDX-License-Identifier: MIT
 
 import os
+import multiprocessing
 import sys
 import subprocess
 import shutil
@@ -27,6 +28,8 @@
 
 languages = build_info.get_languages()
 exit_status = 0
+cores = multiprocessing.cpu_count()
+print('building boards with parallelism {}'.format(cores))
 for board in build_boards:
     bin_directory = "../bin/{}/".format(board)
     os.makedirs(bin_directory, exist_ok=True)
@@ -41,8 +44,8 @@
         # But sometimes a particular language needs to be built from scratch, if, for instance,
         # CFLAGS_INLINE_LIMIT is set for a particular language to make it fit.
         clean_build_check_result = subprocess.run(
-            "make -C ../ports/{port} TRANSLATION={language} BOARD={board} check-release-needs-clean-build | fgrep 'RELEASE_NEEDS_CLEAN_BUILD = 1'".format(
-                port = board_info["port"], language=language, board=board),
+            "make -C ../ports/{port} TRANSLATION={language} BOARD={board} check-release-needs-clean-build -j {cores} | fgrep 'RELEASE_NEEDS_CLEAN_BUILD = 1'".format(
+                port = board_info["port"], language=language, board=board, cores=cores),
             shell=True, stdout=subprocess.PIPE, stderr=subprocess.STDOUT)
         clean_build = clean_build_check_result.returncode == 0