Suppress numerous CMake warnings. Upstream has CMP0071 set to OLD behavior
in the 5.x version, and build fails if set to NEW.

--- CMakeLists.txt.orig	2017-12-23 22:30:29 UTC
+++ CMakeLists.txt
@@ -9,6 +9,9 @@ set(CMAKE_AUTOMOC TRUE)
 
 # cmake 2.6 proposed to add this policy
 if(COMMAND cmake_policy)
+  if(POLICY CMP0071)
+    cmake_policy(SET CMP0071 OLD)
+  endif(POLICY CMP0071)
   if(POLICY CMP0017)
     cmake_policy(SET CMP0017 NEW)
   endif(POLICY CMP0017)