Please specify prototyping behavior for CharWidth.xs (see perlxs manual)
In file included from CharWidth.xs:5:
ppport.h:227:11: warning: ‘PERL_UNUSED_DECL’ redefined
  227 | #  define PERL_UNUSED_DECL
      |           ^~~~~~~~~~~~~~~~
In file included from CharWidth.xs:2:
/usr/lib/perl5/5.42.2/core_perl/CORE/perl.h:539:11: note: this is the location of the previous definition
  539 | #  define PERL_UNUSED_DECL __attribute__unused__
      |           ^~~~~~~~~~~~~~~~