configure script related to compiler flags.

Thanks to Daniel Shaulov for the bug report and patch.

Patch by SilentGhost.

files cannot be written.

Issue #26569: Fix pyclbr.readmodule() and pyclbr.readmodule_ex() to support
importing packages.

Issue #26563: Py_FatalError: disable faulthandler before trying to flush
sys.stdout and sys.stderr.

Issue #26563: Replace PyMem_Malloc() with PyMem_RawFree() since
PostToQueueCallback() calls PyMem_RawFree() (previously PyMem_Free()) in a new
C thread which doesn't hold the GIL.

Issue #26564. Cleanup the code, lineno is never negative.

Issue #26558.

Issue #26558: If Py_FatalError() is called without the GIL, don't try to print
the current exception, nor try to flush stdout and stderr: only dump the
traceback of Python threads.

Patch from Victor van den Elzen.

Ignore pip warning in test_venv.test_with_venv().

Issue #17758: Skip test_site if site.USER_SITE directory doesn't exist and
cannot be created.

#25687: clarify that errors in tearDown increase the total number of reported errors.  Initial patch by HyeSoo Park.

Tamás Bence Gedai.

Patch by Dmitry Shachnev.

NotImplementedError instead of ImportError.

multipliers, not final sizes.  Explain y default for .zoom and .subsample.
Initial patch by Serhiy Storchaka.

* add link to PYTHONMALLOCSTATS env var
* add parameters to PyMem macros like PyMem_MALLOC()
* fix PyMem_SetupDebugHooks(): add Calloc functions
* add some newlines for readability

Added few missed tests for configure options.

Force clean of externals on buildbots.