SCons: respect cache read only (#29437)

* respect readonly

* gitignore and move to correct folder

* also copy old

.gitignore

@@ -5,6 +5,7 @@ venv/
 .tags
 .ipynb_checkpoints
 .idea
+.moc_files
 .overlay_init
 .overlay_consistent
 .sconsign.dblite

SConstruct

@@ -1,4 +1,5 @@
 import os
+import shutil
 import subprocess
 import sys
 import sysconfig
@@ -334,7 +335,18 @@ qt_flags = [
 qt_env['CXXFLAGS'] += qt_flags
 qt_env['LIBPATH'] += ['#selfdrive/ui']
 qt_env['LIBS'] = qt_libs
-qt_env['QT3_MOCHPREFIX'] = cache_dir + '/moc_files/moc_'
+
+# Have to respect cache-readonly
+if GetOption('cache_readonly'):
+  local_moc_files_dir = Dir("#.moc_files").abspath
+  cache_moc_files_dir = cache_dir + "/moc_files"
+  if os.path.exists(local_moc_files_dir):
+    shutil.rmtree(local_moc_files_dir)
+  if os.path.exists(cache_moc_files_dir):
+    shutil.copytree(cache_moc_files_dir, local_moc_files_dir)
+  qt_env['QT3_MOCHPREFIX'] = local_moc_files_dir + "/moc_"
+else:
+  qt_env['QT3_MOCHPREFIX'] = cache_dir + '/moc_files/moc_'
 
 if GetOption("clazy"):
   checks = [