build: add 'lto' to features.txt if built with it

This makes it easy to tell at a glance if a build was with LTO or not.

Change-Id: I7ba9b412f7b74d300a0c55e36ea4cf522d46e6f2

apps/apps.make

@@ -18,6 +18,11 @@ SRC += $(call preprocess, $(APPSDIR)/SOURCES)
 # Kludge: depends on config.o which only depends on config-*.h to have config.h
 # changes trigger a genlang re-run
 #
+
+ifneq (,$(USE_LTO))
+$(BUILDDIR)/apps/features: PPCFLAGS += -DUSE_LTO
+endif
+
 $(BUILDDIR)/apps/features: $(APPSDIR)/features.txt  $(BUILDDIR)/firmware/common/config.o
 	$(SILENT)mkdir -p $(BUILDDIR)/apps
 	$(SILENT)mkdir -p $(BUILDDIR)/lang

apps/features.txt

@@ -308,3 +308,7 @@ perceptual_volume
 #if defined(CODEC_AAC_SBR_DEC)
 codec_aac_he
 #endif
+
+#if defined(USE_LTO)
+lto
+#endif