[Pal] pal.map: Add "DO NOT MODIFY" warning to generated file

Makefile.rules

@@ -148,7 +148,9 @@ PAL_SYMBOL_FILE := $(dir $(abspath $(lastword $(MAKEFILE_LIST))))Pal/src/pal-sym
 PAL_SYMBOLS = $(shell sed -e 's|$$|;|g' $(PAL_SYMBOL_FILE))
 
 quiet_cmd_pal_map = [ $@ ]
-      cmd_pal_map = sed -e 's|\$$(PAL_SYMBOLS)|$(PAL_SYMBOLS)|g' $< > $@
+      cmd_pal_map = \
+	(echo "/* DO NOT MODIFY. THIS FILE WAS AUTO-GENERATED. */"; \
+	 sed -e 's|\$$(PAL_SYMBOLS)|$(PAL_SYMBOLS)|g' $<) > $@
 
 pal.map: pal.map.template $(PAL_SYMBOL_FILE)
 	$(call cmd,pal_map)