tests: simplify detection of Catch v3 for tests

tests/CMakeLists.txt

@@ -1,25 +1,13 @@
 cmake_minimum_required (VERSION 3.8)
 
-# MSYS2 / MinGW uses Catch 3.x.
-if (MINGW)
+include (CheckIncludeFileCXX)
+check_include_file_cxx (catch2/catch_test_macros.hpp HAS_CATCH_V3_HEADER)
+check_include_file_cxx (catch2/catch.hpp HAS_CATCH_V2_HEADER)
+
+if (HAS_CATCH_V3_HEADER AND NOT HAS_CATCH_V2_HEADER)
   set(HAS_CATCH_V3 ON)
 else ()
   set(HAS_CATCH_V3 OFF)
 endif ()
 
-# Some newer distros like Fedora 38+ or Ubuntu 24.04+ also use Catch 3.x.
-if (UNIX AND CMAKE_VERSION VERSION_GREATER_EQUAL "3.22.0")
-  cmake_host_system_information(RESULT DIST_NAME QUERY DISTRIB_NAME)
-  cmake_host_system_information(RESULT DIST_VERSION_ID QUERY DISTRIB_VERSION_ID)
-
-  if (DIST_NAME STREQUAL "Fedora Linux" AND DIST_VERSION_ID VERSION_GREATER_EQUAL "38")
-    # Fedora 38 or later detected, set flag for Catch 3.x.
-    set(HAS_CATCH_V3 ON)
-  endif ()
-  if (DIST_NAME STREQUAL "Ubuntu" AND DIST_VERSION_ID VERSION_GREATER_EQUAL "24.04")
-    # Ubuntu 24.04 or later detected, set flag for Catch 3.x.
-    set(HAS_CATCH_V3 ON)
-  endif ()
-endif()
-
 add_subdirectory (webp-viewer-tests)