cpan_build: Fix cmaker Build.PL module builds

Certain cpan Build.PL based modules were failing to build due to
the host's config information being used instead of the targets.

This patch sets the appropriate variables to ensure the modules
get the correct configuration from the target config_heavy.pl script.

It also ensures the linker is CCLD, not LD since the LDFLAGS contain
-Wl,XXX options and build failures result if LD is used.

libencode-detect-perl is a module which tests this class extensively.

(From OE-Core rev: 7fac8bffcd250aec90c0b675aeb2bbe7896d0ae1)

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

meta/classes/cpan_build.bbclass

@@ -1,7 +1,12 @@
 #
 # This is for perl modules that use the new Build.PL build system
 #
-inherit cpan-base
+inherit cpan-base perlnative
+
+# Env var which tells perl if it should use host (no) or target (yes) settings
+export PERLCONFIGTARGET = "${@is_target(d)}"
+export PERL_ARCHLIB = "${STAGING_LIBDIR}${PERL_OWN_DIR}/perl/${@get_perl_version(d)}"
+export LD = "${CCLD}"
 
 #
 # We also need to have built libmodule-build-perl-native for