Add target to compile to assembly

Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
diff --git a/library/Makefile b/library/Makefile
index e965158..c2e4a2c 100644
--- a/library/Makefile
+++ b/library/Makefile
@@ -346,6 +346,10 @@
 	echo "  CC    $<"
 	$(CC) $(LOCAL_CFLAGS) $(CFLAGS) -o $@ -c $<
 
+.c.s:
+	echo "  CC    $<"
+	$(CC) $(LOCAL_CFLAGS) $(CFLAGS) -S -o $@ -c $<
+
 .PHONY: generated_files
 generated_files: $(GENERATED_FILES)