added m4 to prereq check, thanks to Gerph

SVN-Revision: 15043

include/prereq-build.mk

@@ -148,3 +148,7 @@ endef
 $(eval $(call Require,getopt-extended, \
 	Please install an extended getopt version that supports --long \
 ))
+
+$(eval $(call RequireCommand,m4, \
+	Please install GNU m4 \
+))