Fix compatibility with CMake 3.5

CMakeLists.txt

@@ -39,11 +39,17 @@ endif()
 project(Catch2
   VERSION 3.1.0 # CML version placeholder, don't delete
   LANGUAGES CXX
-  # HOMEPAGE_URL is not supported until CMake version 3.12, which
-  # we do not target yet.
-  # HOMEPAGE_URL "https://github.com/catchorg/Catch2"
-  DESCRIPTION "A modern, C++-native, unit test framework."
 )
+# DESCRIPTION and HOMEPAGE_URL are not supported in CMake 3.5 as arguments
+# to project(). We set them manually.
+set(PROJECT_DESCRIPTION "A modern, C++-native, unit test framework.")
+set(${PROJECT_NAME}_DESCRIPTION "${PROJECT_DESCRIPTION}")
+set(PROJECT_HOMEPAGE_URL "https://github.com/catchorg/Catch2")
+set(${PROJECT_NAME}_HOMEPAGE_URL "${PROJECT_HOMEPAGE_URL}")
+if (NOT_SUBPROJECT)
+    set(CMAKE_PROJECT_DESCRIPTION "${PROJECT_DESCRIPTION}")
+    set(CMAKE_PROJECT_HOMEPAGE_URL "${PROJECT_HOMEPAGE_URL}")
+endif()
 
 
 # Provide path for scripts. We first add path to the scripts we don't use,