We now build GLEW always (unless a system one is used)

So its headers are always there in workdir.

Change-Id: I513b49da52c1f393c02b24c5bcf0f415e22e79d2

RepositoryExternal.mk

@@ -228,10 +228,7 @@ endef
 
 endif # SYSTEM_CPPUNIT
 
-ifeq ($(filter FREEBSD LINUX MACOSX WNT,$(OS)),)
-gb_LinkTarget__use_glew :=
-
-else ifneq ($(SYSTEM_GLEW),)
+ifneq ($(SYSTEM_GLEW),)
 
 define gb_LinkTarget__use_glew
 $(call gb_LinkTarget_set_include,$(1),\