gh-105776: Fix test_cppext when CC contains -std=c11 option

[vstinner]

• Issue: Python 3.11.4: Running "make test" fails under gcc 4.8.5 because both -std=gnu11 and -std=c++11 are specified when compiling _testcpp11ext #105776

[vstinner]

Without this PR, test_cppext fails with these commands:

$ ./configure --with-pydebug 'CC=gcc -std=c11' CFLAGS="-O0"
$ make
$ ./python -m test test_cppext -v

With this PR, test_cppext pass.

[miss-islington]

Thanks @vstinner for the PR 🌮🎉.. I'm working now to backport this PR to: 3.11, 3.12.
🐍🍒⛏🤖

[miss-islington]

Sorry, @vstinner, I could not cleanly backport this to 3.11 due to a conflict.
Please backport using cherry_picker on command line.
cherry_picker 9173b2bbe13aeccc075b571da05c653a2a91de1b 3.11

[bedevere-bot]

GH-108345 is a backport of this pull request to the 3.12 branch.

[bedevere-bot]

GH-108347 is a backport of this pull request to the 3.11 branch.

[bedevere-bot]

⚠️⚠️⚠️ Buildbot failure ⚠️⚠️⚠️

Hi! The buildbot AMD64 Fedora Stable 3.x has failed when building commit 9173b2b.

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/543/builds/4279) and take a look at the build logs.
4. Check if the failure is related to this commit (9173b2b) 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/543/builds/4279

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

== Tests result: ENV CHANGED ==

432 tests OK.

10 slowest tests:

• test_gdb: 4 min 29 sec
• test_multiprocessing_spawn: 3 min 7 sec
• test_concurrent_futures: 2 min 49 sec
• test_math: 2 min 33 sec
• test_multiprocessing_forkserver: 1 min 39 sec
• test_multiprocessing_fork: 1 min 13 sec
• test_tokenize: 1 min 7 sec
• test_capi: 1 min 3 sec
• test_unparse: 1 min
• test_socket: 55.5 sec

1 test altered the execution environment:
test_ssl

14 tests skipped:
test.test_asyncio.test_windows_events
test.test_asyncio.test_windows_utils test_devpoll test_ioctl
test_kqueue test_launcher test_startfile test_tkinter test_ttk
test_winconsoleio test_winreg test_winsound test_wmi
test_zipfile64

Total duration: 5 min 24 sec

Click to see traceback logs

remote: Enumerating objects: 20, done.        
remote: Counting objects:   5% (1/20)        
remote: Counting objects:  10% (2/20)        
remote: Counting objects:  15% (3/20)        
remote: Counting objects:  20% (4/20)        
remote: Counting objects:  25% (5/20)        
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remote: Counting objects:  35% (7/20)        
remote: Counting objects:  40% (8/20)        
remote: Counting objects:  45% (9/20)        
remote: Counting objects:  50% (10/20)        
remote: Counting objects:  55% (11/20)        
remote: Counting objects:  60% (12/20)        
remote: Counting objects:  65% (13/20)        
remote: Counting objects:  70% (14/20)        
remote: Counting objects:  75% (15/20)        
remote: Counting objects:  80% (16/20)        
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remote: Counting objects:  90% (18/20)        
remote: Counting objects:  95% (19/20)        
remote: Counting objects: 100% (20/20)        
remote: Counting objects: 100% (20/20), done.        
remote: Compressing objects:  20% (1/5)        
remote: Compressing objects:  40% (2/5)        
remote: Compressing objects:  60% (3/5)        
remote: Compressing objects:  80% (4/5)        
remote: Compressing objects: 100% (5/5)        
remote: Compressing objects: 100% (5/5), done.        
remote: Total 11 (delta 9), reused 7 (delta 6), pack-reused 0        
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HEAD is now at 9173b2bbe1 gh-105776: Fix test_cppext when CC contains -std=c11 option (#108343)
Switched to and reset branch 'main'

../Objects/longobject.c: In function ‘long_format_binary’:
../Objects/longobject.c:2122:13: warning: ‘kind’ may be used uninitialized [-Wmaybe-uninitialized]
 2122 |     else if (kind == PyUnicode_1BYTE_KIND) {
      |             ^
../Objects/longobject.c:1998:9: note: ‘kind’ was declared here
 1998 |     int kind;
      |         ^~~~
../Objects/longobject.c: In function ‘long_to_decimal_string_internal’:
../Objects/longobject.c:1945:13: warning: ‘kind’ may be used uninitialized [-Wmaybe-uninitialized]
 1945 |     else if (kind == PyUnicode_1BYTE_KIND) {
      |             ^
../Objects/longobject.c:1769:9: note: ‘kind’ was declared here
 1769 |     int kind;
      |         ^~~~

make: *** [Makefile:2034: buildbottest] Error 3