Testing on Windows occasionally has issues in test_compileall when running with multiple processes.  This is due to other test files importing stdlib modules at the same time that compileall is doing its own testing.  While not fatal (test_compileall succeeds on re-run), the transient warnings obfuscate the test results for other "real" warnings (e.g., compiler warnings) without digging into each run separately.

This can be avoided by using the PYTHONPYCACHEPREFIX functionality to compile the stdlib modules locally.