Fix compilation with -Wunused-variable

[attilaolah]

When compiling with -Wunused-variable, EXT_STRERROR_R_CHAR_P gets undefined because of a failing compilation check.

An alternative would be to return c ? 0 : 0, which works with compilers that do not have __attribute__((undefined)), but recent compilers seem to support this and the __attribute__ approach seems cleaner.

[kmilos]

Don't think this'll fly w/ MSVC, right? Inserting (void)c; doesn't work?

Then again, looks like strerror_r is not available in Windows anyway, but still nicer to have the test fail because of the actual missing method rather than the compiler...

[attilaolah]

Good point, (void)c works too. I'll update this PR.

[attilaolah]

PTAL.

[codecov]

Codecov Report

Merging #1714 (33419c8) into main (19000cd) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             main    #1714   +/-   ##
=======================================
  Coverage   66.89%   66.89%           
=======================================
  Files         151      151           
  Lines       20761    20761           
=======================================
  Hits        13889    13889           
  Misses       6872     6872           

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[hassec]

LGTM! Thanks for the contribution! 👍

[hassec]

@Mergifyio backport 0.27-maintenance

[mergify]

Command backport 0.27-maintenance: success

Backports have been created

• #1728 Fix compilation with -Wunused-variable (backport #1714) has been created for branch 0.27-maintenance