Perl, at build time, get errno numbers of the system in a similar way[0]: preprocess errno.h with `$CC -E` and recursively scan all files in # markers for macro

Perl, at build time, get errno numbers of the system in a similar way[0]: preprocess errno.h with `$CC -E` and recursively scan all files in # markers for macro defines. The configure script even checks the existence of several system headers this way, so if your C compiler don't support # markers in -E output, you get missing includes everywhere. [0] https://github.com/Perl/perl5/blob/blead/ext/Errno/Errno_pm.PL https://github.com/Perl/perl5/blob/blead/ext/Errno/Errno_pm....