Add -flto to CXXFLAGS

Per openbmc/openbmc#3364, adding -flto to CXX flags
in order to reduce overall library and binary sizes.

Ref: https://gcc.gnu.org/wiki/LinkTimeOptimization

Tested: Verified it compiled and booted to Ready in QEMU

Change-Id: I64ffa450d8cd964e01d78ce5bbc97b93df47509d
Signed-off-by: Andrew Geissler <geissonator@yahoo.com>
diff --git a/Makefile.am b/Makefile.am
index cb1271e..89692de 100755
--- a/Makefile.am
+++ b/Makefile.am
@@ -32,7 +32,8 @@
 	$(SYSTEMD_CFLAGS) \
 	$(PHOSPHOR_DBUS_INTERFACES_CFLAGS) \
 	$(SDBUSPLUS_CFLAGS) \
-	$(PHOSPHOR_LOGGING_CFLAGS)
+	$(PHOSPHOR_LOGGING_CFLAGS) \
+	-flto
 generic_ldflags = \
 	$(SYSTEMD_LIBS) \
 	$(PHOSPHOR_DBUS_INTERFACES_LIBS) \