Policy 0063 must be enabled to have hidden inline visibility... (#900)

...on static builds.

CMakeLists.txt

diff --git a/CMakeLists.txt b/CMakeLists.txt
index 85709b2..a41afc4 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -1,4 +1,6 @@
 cmake_minimum_required(VERSION 2.8.0)
+cmake_policy(SET CMP0063 NEW)
+
 project(harfbuzz)
 
 enable_testing()