Fix scope of CMake Policy variables

Commit 7d47760 ("moving some settings to an apposite cmake file")
moved the `cmake_policy(SET CMP0072 NEW)` from the toplevel scope to the
scope of the included file. For details, see
https://cmake.org/cmake/help/latest/manual/cmake-policies.7.html

Set NO_POLICY_SCOPE when including the file, to move the POLICIES back
to the toplevel scope. Also remove the extra cmake_minimum_version from
external/CMakeLists.txt, as it implicitly calls
`cmake_policy(VERSION 3.10)`, resetting any policies introduced with
cmake 3.11 and newer (i.e. CMP0072 and CMP0077).

Fixes cnr-isti-vclab#1095.

src/CMakeLists.txt

@@ -18,7 +18,7 @@ option(MESHLAB_IS_NIGHTLY_VERSION "Nightly version of meshlab will be used inste
 
 ### Dependencies
 list(APPEND CMAKE_MODULE_PATH "${CMAKE_CURRENT_SOURCE_DIR}/cmake")
-include("${CMAKE_CURRENT_SOURCE_DIR}/cmake/meshlab_global_settings.cmake")
+include("${CMAKE_CURRENT_SOURCE_DIR}/cmake/meshlab_global_settings.cmake" NO_POLICY_SCOPE)
 include("${CMAKE_CURRENT_SOURCE_DIR}/cmake/meshlab_tools.cmake")
 
 #message(STATUS "Searching for required components")

src/cmake/meshlab_global_settings.cmake

@@ -8,7 +8,9 @@ if(POLICY CMP0072)
 endif()
 
 #enable setting options with SET cmake command
-set(CMAKE_POLICY_DEFAULT_CMP0077 NEW)
+if(POLICY CMP0077)
+	cmake_policy(SET CMP0077 NEW)
+endif()
 
 ### Build settings
 set(CMAKE_C_STANDARD 99)

src/external/CMakeLists.txt

@@ -2,8 +2,6 @@
 # Copyright 2019, 2020, Visual Computing Lab, ISTI - Italian National Research Council
 # SPDX-License-Identifier: BSL-1.0
 
-cmake_minimum_required(VERSION 3.10)
-
 option(
 	ALLOW_OPTIONAL_EXTERNAL_MESHLAB_LIBRARIES
 	"Allow to use/build optional external libraries"