PATCH: [perl #38193] embedded perl always calls setlocale(LC_ALL,"")

This commit causes the locale initialization to skip calling
setlocal(foo, "") if the environment variable PERL_SKIP_LOCALE_INIT is
set.  Instead, the setup code calls setlocale(LC_ALL, NULL) (plus other
similar calls for the subcategories) in order to find out what the
current locale is.

The original poster for this ticket has a workaround for it which
involves using a modified copy of Perl core code.  This patch defines
the C preprocessor variable HAS_SKIP_LOCALE_INIT that can be used by XS
writers to discover if the current Perl version needs the workaround or
not.

I was unable to come up with a test for this patch that did not involve
building extensive infrastructure for testing embedded Perl.  That does
not seem worth it for such a trivial patch.  I tested by hand.
locale documentation: Grammaar and appearance nits