[Perl/perl5] 9302e8: ensure types of PL_nan and PL_inf are consistent

[Tony Cook via perl5-changes]

  Branch: refs/heads/blead
  Home:   https://github.com/Perl/perl5
  Commit: 9302e8db483378404025d881979158d1eb6edc05
      
https://github.com/Perl/perl5/commit/9302e8db483378404025d881979158d1eb6edc05
  Author: Tony Cook <t...@develop-help.com>
  Date:   2021-06-24 (Thu, 24 Jun 2021)

  Changed paths:
    M perl.h

  Log Message:
  -----------
  ensure types of PL_nan and PL_inf are consistent

Different types for a variable across compilation units can in
theory cause undefined behavior.  In this case I think it's unlikely
to cause an issue, but LTO builds also (correctly) complain about
the type mismatch, so ensure they match.