move platform.mk out from makefile

platform.mk

@@ -0,0 +1,34 @@
+PLAT ?= none
+PLATS = linux freebsd macosx
+
+CC ?= gcc
+
+.PHONY : none $(PLATS) clean all
+
+ifneq ($(PLAT), none)
+
+.PHONY : default
+
+default :
+	$(MAKE) $(PLAT)
+
+endif
+
+none :
+	@echo "Please do 'make PLATFORM' where PLATFORM is one of these:"
+	@echo "   $(PLATS)"
+
+LIBS := -lpthread -lm
+SHARED := -fPIC --shared
+EXPORT := -Wl,-E
+
+$(PLATS) : all 
+
+linux : PLAT = linux
+macosx : PLAT = macosx
+freebsd : PLAT = freebsd
+
+macosx linux : LIBS += -ldl
+macosx : SHARED := -fPIC -dynamiclib -Wl,-undefined,dynamic_lookup
+macosx : EXPORT :=
+linux freebsd : LIBS += -lrt