[build] check xcode command line tools version >= 6

future-proof version check for BLAS libraries on OS X
fix BVLC#3092

Author: shelhamer

Makefile

@@ -354,8 +354,9 @@ else
 		# OS X packages atlas as the vecLib framework
 		LIBRARIES += cblas
 		# 10.10 has accelerate while 10.9 has veclib
-		XCODE_CLT_VER := $(shell pkgutil --pkg-info=com.apple.pkg.CLTools_Executables | grep -o 'version: 6')
-		ifneq (,$(findstring version: 6,$(XCODE_CLT_VER)))
+		XCODE_CLT_VER := $(shell pkgutil --pkg-info=com.apple.pkg.CLTools_Executables | grep 'version' | sed 's/[^0-9]*\([0-9]\).*/\1/')
+		XCODE_CLT_GEQ_6 := $(shell [ $(XCODE_CLT_VER) -gt 5 ] && echo 1)
+		ifeq ($(XCODE_CLT_GEQ_6), 1)
 			BLAS_INCLUDE ?= /System/Library/Frameworks/Accelerate.framework/Versions/Current/Frameworks/vecLib.framework/Headers/
 			LDFLAGS += -framework Accelerate
 		else