do not report context on python traceback, for PermissionError

It's not a MesonBug which needs to be reported, and the existing error
already adequately points out the problematic file.

It is impossible to get a PermissionError for files created by meson
itself, once the build directory has been created, anyway.

mesonbuild/mesonmain.py

@@ -152,6 +152,11 @@ class CommandLineParser:
             if os.environ.get('MESON_FORCE_BACKTRACE'):
                 raise
             return 1
+        except PermissionError:
+            if os.environ.get('MESON_FORCE_BACKTRACE'):
+                raise
+            traceback.print_exc()
+            return 2
         except Exception as e:
             if os.environ.get('MESON_FORCE_BACKTRACE'):
                 raise