FWIW this change builds up to a build system refactor that fixes some bugs/quirks with BOLT and enables the use of BOLT on libpython, which results in significant pyperformance impact. The remaining rough set of commits are available in #101093.

LGTM with nit comment But for future work, I would like to say. For the BOLT, it could also be able to be enabled without enabling PGO. (Might be a weird configuration, but someone may need it)

Agree that we should support {none, either, both} configs. But it may require a bit of work to get there. I'll keep this in mind and try to implement it. I think the refactoring I'm doing to the PGO/BOLT make rules should make this vastly easier to achieve.

⚠️⚠️⚠️ Buildbot failure ⚠️⚠️⚠️

Hi! The buildbot wasm32-emscripten node (dynamic linking) 3.x has failed when building commit 27d8ecd.

What do you need to do:

1. Don't panic.
2. Check the buildbot page in the devguide if you don't know what the buildbots are or how they work.
3. Go to the page of the buildbot that failed (https://buildbot.python.org/all/#builders/1056/builds/2009) and take a look at the build logs.
4. Check if the failure is related to this commit (27d8ecd) or if it is a false positive.
5. If the failure is related to this commit, please, reflect that on the issue and make a new Pull Request with a fix.

You can take a look at the buildbot page here:

https://buildbot.python.org/all/#builders/1056/builds/2009

Failed tests:

• test_bytes

Summary of the results of the build (if available):

== Tests result: FAILURE ==

335 tests OK.

10 slowest tests:

• test_hashlib: 2 min 2 sec
• test_math: 1 min 48 sec
• test_tokenize: 1 min 13 sec
• test_unparse: 47.8 sec
• test_lib2to3: 45.5 sec
• test_capi: 32.6 sec
• test_tarfile: 25.0 sec
• test_fstring: 23.6 sec
• test_unicodedata: 21.4 sec
• test_pickle: 17.0 sec

1 test failed:
test_bytes

127 tests skipped:
test.test_asyncio.test_base_events
test.test_asyncio.test_buffered_proto
test.test_asyncio.test_context
test.test_asyncio.test_eager_task_factory
test.test_asyncio.test_events test.test_asyncio.test_futures
test.test_asyncio.test_futures2 test.test_asyncio.test_locks
test.test_asyncio.test_pep492
test.test_asyncio.test_proactor_events
test.test_asyncio.test_protocols test.test_asyncio.test_queues
test.test_asyncio.test_runners
test.test_asyncio.test_selector_events
test.test_asyncio.test_sendfile test.test_asyncio.test_server
test.test_asyncio.test_sock_lowlevel test.test_asyncio.test_ssl
test.test_asyncio.test_sslproto test.test_asyncio.test_streams
test.test_asyncio.test_subprocess
test.test_asyncio.test_taskgroups test.test_asyncio.test_tasks
test.test_asyncio.test_threads test.test_asyncio.test_timeouts
test.test_asyncio.test_transports
test.test_asyncio.test_unix_events test.test_asyncio.test_waitfor
test.test_asyncio.test_windows_events
test.test_asyncio.test_windows_utils test__xxinterpchannels
test__xxsubinterpreters test_asyncgen test_clinic test_cmd_line
test_concurrent_futures test_contextlib_async test_ctypes
test_curses test_dbm_gnu test_dbm_ndbm test_devpoll test_doctest
test_docxmlrpc test_dtrace test_embed test_epoll test_faulthandler
test_fcntl test_file_eintr test_fork1 test_ftplib test_gdb
test_grp test_httplib test_httpservers test_idle test_imaplib
test_interpreters test_ioctl test_kqueue test_launcher test_lzma
test_mmap test_msilib test_multiprocessing_fork
test_multiprocessing_forkserver test_multiprocessing_main_handling
test_multiprocessing_spawn test_nis test_openpty test_ossaudiodev
test_pdb test_peg_generator test_perf_profiler test_poll
test_poplib test_pty test_pwd test_queue test_readline
test_regrtest test_repl test_resource test_select test_selectors
test_smtplib test_smtpnet test_socket test_socketserver test_spwd
test_ssl test_stable_abi_ctypes test_startfile test_subprocess
test_sys_settrace test_syslog test_tcl test_telnetlib test_thread
test_threadedtempfile test_threading test_threading_local test_tix
test_tkinter test_tools test_ttk test_ttk_textonly test_turtle
test_urllib2 test_urllib2_localnet test_urllib2net test_urllibnet
test_venv test_wait3 test_wait4 test_webbrowser test_winconsoleio
test_winreg test_winsound test_wmi test_wsgiref test_xmlrpc
test_xmlrpc_net test_zipfile64 test_zipimport_support
test_zoneinfo
0:25:49 load avg: 10.37
0:25:49 load avg: 10.37 Re-running failed tests is not supported with --python host runner option.

Total duration: 25 min 49 sec

Post-merge review: LGTM

@indygreg: please don't force-push; it does not play well with reviews on GitHub. If you haven't already, please take a look at the devguide, specifically Life of a Pull Request