fix PERL_VERSION_xx comparison macros

[mauke]

• Fix PERL_VERSION_EQ(x, y, '*') and PERL_VERSION_NE(x, y, '*') by using the correct helper constants (D_PPP_VERSION_MAJOR and D_PPP_VERSION_MINOR don't exist)
• Fix PERL_VERSION_LE and PERL_VERSION_GT; these used to claim that for all versions X, X > X and !(X <= X). See https://github.com/Perl/perl5/issues/21506.
• Add unit tests.

[mauke]

Closing this as an equivalent patch has been merged into blead: https://github.com/Perl/perl5/commit/70d391de2d922d20c97ccb9b93f01d86633f082d