perl/Makefile.PL: detect MakeMaker versions incompatible with DESTDIR

It appears that ExtUtils::MakeMaker versions older than 6.11 do not
implement the DESTDIR mechanism.  So add a test to the generated perl.mak
to detect when DESTDIR is used along with a too old ExtUtils::MakeMaker and
abort with a message suggesting the use of NO_PERL_MAKEMAKER.

Signed-off-by: Brandon Casey <casey@nrlssc.navy.mil>
Signed-off-by: Shawn O. Pearce <spearce@spearce.org>

perl/Makefile.PL

@@ -5,6 +5,14 @@ sub MY::postamble {
 instlibdir:
 	@echo '$(INSTALLSITELIB)'
 
+ifneq (,$(DESTDIR))
+ifeq (0,$(shell expr '$(MM_VERSION)' '>' 6.10))
+$(error ExtUtils::MakeMaker version "$(MM_VERSION)" is older than 6.11 and so \
+	is likely incompatible with the DESTDIR mechanism.  Try setting \
+	NO_PERL_MAKEMAKER=1 instead)
+endif
+endif
+
 MAKE_FRAG
 }