Optimize Makefile.

Don't do recursive makes for COMPARE and MODERN, use minimal makefile for making tools.

make_tools.mk

@@ -0,0 +1,12 @@
+
+TOOLDIRS := $(filter-out tools/agbcc tools/binutils,$(wildcard tools/*))
+TOOLBASE = $(TOOLDIRS:tools/%=%)
+TOOLS = $(foreach tool,$(TOOLBASE),tools/$(tool)/$(tool)$(EXE))
+
+.PHONY: all $(TOOLDIRS)
+
+all: $(TOOLDIRS)
+	@:
+
+$(TOOLDIRS):
+	@$(MAKE) -C $@