fix up LDFLAGS and CXXFLAGS for pel extension

Went to add a new flag to CXXFLAGS and realized it was not being used at
all during build.

Signed-off-by: Andrew Geissler <geissonator@yahoo.com>
Change-Id: I11dce1e7ab451736a0e9afc19095810974da5af5
diff --git a/extensions/openpower-pels/openpower-pels.mk b/extensions/openpower-pels/openpower-pels.mk
index e510b42..d18947e 100644
--- a/extensions/openpower-pels/openpower-pels.mk
+++ b/extensions/openpower-pels/openpower-pels.mk
@@ -59,6 +59,8 @@
 	$(SDEVENTPLUS_CFLAGS) \
 	$(PHOSPHOR_DBUS_INTERFACES_CFLAGS)
 
+libpel_la_CXXFLAGS = $(libpel_cxx_flags)
+
 registrydir = $(datadir)/phosphor-logging/pels/
 registry_DATA = extensions/openpower-pels/registry/message_registry.json