Unused code warning in `_testembed.c`

[sobolevn]

Bug report

Link: https://github.com/python/cpython/actions/runs/11333284963/job/31517440086#step:6:1315

Report:

./Programs/_testembed.c:1904:5: warning: code will never be executed [-Wunreachable-code]
    const char *err_msg;
    ^~~~~~~~~~~~~~~~~~~~
sed -e "s,/usr/bin/env python3,/usr/local/bin/python3.14," < ./Tools/scripts/pydoc3 > build/scripts-3.14/pydoc3.14
./Programs/_testembed.c:2052:5: warning: code will never be executed [-Wunreachable-code]
    const char *err_msg;
sed -e "s,@EXENAME@,/usr/local/bin/python3.14," < ./Misc/python-config.in >python-config.py
    ^~~~~~~~~~~~~~~~~~~~

Source of problem:

• We cannot have goto targets on variable declarations.
• So, they are declared right above:

  cpython/Programs/_testembed.c

  Lines 1903 to 1910 in cc5a225

  	return 0;
  	const char *err_msg;
  	error:
  	(void)PyInitConfig_GetError(config, &err_msg);
  	printf("Python init failed: %s\n", err_msg);
  	exit(1);
  	}

• So, this warning marks const char *err_msg; as unreachable code

I propose to declare this variable before the first goto. This way we can remove this warning. And since this is just a test, we can do that freely.

Linked PRs

• gh-125517: Fix unreachable code warnings in _testembed.c #125518

[vstinner]

On Fedora 40 with clang 18.1.8, I get the following warning:

./Programs/_testembed.c:1906:5: warning: label followed by a declaration is a C23 extension [-Wc23-extensions]
 1906 |     const char *err_msg;
      |     ^
1 warning generated.