Set CMake policies for newer versions of CMake

Make sure that CMP0012 is set to NEW, without which FindPython3 and
FindPython2 functionality becomes broken with CMake 3.18.2 if searching
by location. CMP0012 being set to OLD is also deprecated as of 3.18.3.
Ensure CMP0011 is set to NEW to avoid warnings and deprecated behaviour
being issued about policy push / pop with CMake 3.18.0 or newer.

Signed-off-by: Paul Elliott <[email protected]>

Author: paul-elliott-arm

CMakeLists.txt

@@ -21,6 +21,18 @@
 #
 
 cmake_minimum_required(VERSION 2.8.12)
+
+# https://cmake.org/cmake/help/latest/policy/CMP0011.html
+# Setting this policy is required in CMake >= 3.18.0, otherwise a warning is generated. The OLD
+# policy setting is deprecated, and will be removed in future versions.
+cmake_policy(SET CMP0011 NEW)
+# https://cmake.org/cmake/help/latest/policy/CMP0012.html
+# Setting the CMP0012 policy to NEW is required for FindPython3 to work with CMake 3.18.2
+# (there is a bug in this particular version), otherwise, setting the CMP0012 policy is required
+# for CMake versions >= 3.18.3 otherwise a deprecated warning is generated. The OLD policy setting
+# is deprecated and will be removed in future versions.
+cmake_policy(SET CMP0012 NEW)
+
 if(TEST_CPP)
     project("mbed TLS" C CXX)
 else()