fix a build issue

package/libglew/patches/patch-Makefile

@@ -1,5 +1,14 @@
 --- glew-1.13.0.orig/Makefile	2015-08-10 13:47:22.000000000 +0200
-+++ glew-1.13.0/Makefile	2015-11-09 00:30:11.275929451 +0100
++++ glew-1.13.0/Makefile	2016-01-03 21:31:43.903657870 +0100
+@@ -31,7 +31,7 @@
+ include config/version
+ 
+ SHELL = /bin/sh
+-SYSTEM ?= $(shell config/config.guess | cut -d - -f 3 | sed -e 's/[0-9\.]//g;')
++SYSTEM ?= $(shell sh config/config.guess | cut -d - -f 3 | sed -e 's/[0-9\.]//g;')
+ SYSTEM.SUPPORTED = $(shell test -f config/Makefile.$(SYSTEM) && echo 1)
+ 
+ ifeq ($(SYSTEM.SUPPORTED), 1)
 @@ -77,7 +77,8 @@ else
  OPT = $(POPT)
  endif