Move GLog/GFlags to extern/

This is where the libraries belongs to actually, they are not only used by
Libmv now, but also by tests and Cycles.

CMakeLists.txt

@@ -2585,6 +2585,21 @@ if(WITH_PYTHON_MODULE)
 	add_definitions(-DPy_ENABLE_SHARED)
 endif()
 
+#-----------------------------------------------------------------------------
+# Configure GLog/GFlags
+
+if(WITH_LIBMV OR WITH_GTESTS OR (WITH_CYCLES AND WITH_CYCLES_LOGGING))
+	set(GLOG_DEFINES
+		-DGOOGLE_GLOG_DLL_DECL=
+	)
+
+	set(GFLAGS_DEFINES
+		-DGFLAGS_DLL_DEFINE_FLAG=
+		-DGFLAGS_DLL_DECLARE_FLAG=
+		-DGFLAGS_DLL_DECL=
+	)
+endif()
+
 #-----------------------------------------------------------------------------
 # Extra compile flags