Detect operating system in Makefile.

Makefile

# Detect operating system in Makefile.
# Author: He Tao
# Date: 2015-05-30

OSFLAG 				:=
ifeq ($(OS),Windows_NT)
	OSFLAG += -D WIN32
	ifeq ($(PROCESSOR_ARCHITECTURE),AMD64)
		OSFLAG += -D AMD64
	endif
	ifeq ($(PROCESSOR_ARCHITECTURE),x86)
		OSFLAG += -D IA32
	endif
else
	UNAME_S := $(shell uname -s)
	ifeq ($(UNAME_S),Linux)
		OSFLAG += -D LINUX
	endif
	ifeq ($(UNAME_S),Darwin)
		OSFLAG += -D OSX
	endif
		UNAME_P := $(shell uname -p)
	ifeq ($(UNAME_P),x86_64)
		OSFLAG += -D AMD64
	endif
		ifneq ($(filter %86,$(UNAME_P)),)
	OSFLAG += -D IA32
		endif
	ifneq ($(filter arm%,$(UNAME_P)),)
		OSFLAG += -D ARM
	endif
endif

all:
	@echo $(OSFLAG)