Add native and cross compiling CMake build support

Makefile

@@ -0,0 +1,41 @@
+# makefile discription.
+# basic build file for mruby
+
+# compiler, linker (gcc)
+CC = gcc
+LL = gcc
+DEBUG_MODE = 1
+ifeq ($(DEBUG_MODE),1)
+CFLAGS = -g -O3
+else
+CFLAGS = -O3
+endif
+ALL_CFLAGS = -Wall -Werror-implicit-function-declaration $(CFLAGS)
+ifeq ($(OS),Windows_NT)
+  MAKE_FLAGS = --no-print-directory CC=$(CC) LL=$(LL) ALL_CFLAGS='$(ALL_CFLAGS)'
+else
+  MAKE_FLAGS = --no-print-directory CC='$(CC)' LL='$(LL)' ALL_CFLAGS='$(ALL_CFLAGS)'
+endif
+
+##############################
+# generic build targets, rules
+
+.PHONY : all
+all :
+	@$(MAKE) -C src $(MAKE_FLAGS)
+	@$(MAKE) -C mrblib $(MAKE_FLAGS)
+	@$(MAKE) -C tools/mruby $(MAKE_FLAGS)
+	@$(MAKE) -C tools/mirb $(MAKE_FLAGS)
+
+# mruby test
+.PHONY : test
+test : all
+	@$(MAKE) -C test $(MAKE_FLAGS)
+
+# clean up
+.PHONY : clean
+clean :
+	@$(MAKE) clean -C src $(MAKE_FLAGS)
+	@$(MAKE) clean -C tools/mruby $(MAKE_FLAGS)
+	@$(MAKE) clean -C tools/mirb $(MAKE_FLAGS)
+	@$(MAKE) clean -C test $(MAKE_FLAGS)