Problem reported by Bruno Haible in:
https://lists.gnu.org/r/bug-gnulib/2024-08/msg00085.html
* lib/error.c (verror, verror_at_line) [!_LIBC]: #undef only if
the corresponding GNULIB_defined_... macros are defined.
* lib/error.in.h (verror, verror_with_line):
Don't define as macros if they are already defined, or if
_GL_NO_INLINE_ERROR is defined. This may lose some niceties with GCC
warnings, but the code’s valid.