Added fixes for Google Test reported by AppVeyor

Author: Mikolaj Malecki

CMakeLists.txt

@@ -1682,7 +1682,11 @@ if (ENABLE_UNITTESTS)
 
 	set_tests_properties(${tests_srt} PROPERTIES RUN_SERIAL TRUE)
 	if (ENABLE_UNITTESTS_DISCOVERY)
-		gtest_discover_tests(test-srt)
+		if (NOT COMMAND gtest_discover_tests)
+			message(WARNING "No command gtest_discover_tests provided by GTtest; no test discovery")
+		else ()
+			gtest_discover_tests(test-srt)
+		endif()
 	endif()
 
 	enable_testing()

scripts/googletest-download.cmake

@@ -1,7 +1,7 @@
 # code copied from https://crascit.com/2015/07/25/cmake-gtest/
-cmake_minimum_required(VERSION 2.8.12 FATAL_ERROR)
+cmake_minimum_required(VERSION 3.10 FATAL_ERROR)
 
-project(googletest-download NONE)
+project(GOOGLETEST_DOWNLOAD)
 
 include(ExternalProject)