Change the way Perl modules are installed, update the default Perl to 5.18.

Before, we had:

  site_perl :           lib/perl5/site_perl/5.18
  site_perl/perl_arch : lib/perl5/site_perl/5.18/mach
  perl_man3 :           lib/perl5/5.18/man/man3

Now we have:

  site_perl : lib/perl5/site_perl
  site_arch : lib/perl5/site_perl/mach/5.18
  perl_man3 : lib/perl5/site_perl/man/man3

Modules without any .so will be installed at the same place regardless of the
Perl version, minimizing the upgrade when the major Perl version is changed.
It uses a version dependent directory for modules with compiled bits.

As PERL_ARCH is no longer needed in plists, it has been removed from
PLIST_SUB.

The USE_PERL5=fixpacklist keyword is removed, the .packlist file is now
always removed, as is perllocal.pod.

The old site_perl and site_perl/arch directories have been kept in the
default Perl @INC for all Perl ports, and will be phased out as these old
Perl versions expire.

PR:		194969
Differential Revision:	https://reviews.freebsd.org/D1019
Exp-run by:	antoine
Reviewed by:	perl@
Approved by:	portmgr

math/p5-Math-Int128/Makefile

@@ -3,6 +3,7 @@
 
 PORTNAME=	Math-Int128
 PORTVERSION=	0.15
+PORTREVISION=	1
 CATEGORIES=	math perl5
 MASTER_SITES=	CPAN
 PKGNAMEPREFIX=	p5-
@@ -30,6 +31,6 @@ USE_GCC=	yes
 .endif
 
 post-stage:
-	${STRIP_CMD} ${STAGEDIR}${SITE_PERL}/${PERL_ARCH}/auto/Math/Int128/Int128.so
+	${STRIP_CMD} ${STAGEDIR}${PREFIX}/${SITE_ARCH_REL}/auto/Math/Int128/Int128.so
 
 .include <bsd.port.post.mk>