Tests: Revert workaround for COMPILE_FEATURES genex bug

The second hunk of commit 07d1f6fc (Features: Properly evaluate if the
compiler supports cxx_final, 2014-12-31) was a workaround for a bug in
the COMPILE_FEATURES generator expression that caused it never to return
0.  Revert the workaround so we can fix the bug instead.

Tests/RunCMake/CompileFeatures/NonValidTarget1.cmake

@@ -11,7 +11,7 @@ add_custom_command(OUTPUT "${CMAKE_CURRENT_BINARY_DIR}/copied_file${expected_res
   COMMAND "${CMAKE_COMMAND}" -E copy "${CMAKE_CURRENT_SOURCE_DIR}/empty.cpp" "${CMAKE_CURRENT_BINARY_DIR}/copied_file${genexvar}.cpp"
 )
 
-add_library(empty "${CMAKE_CURRENT_BINARY_DIR}/copied_file${expected_result}.cpp")
+add_library(empty "${CMAKE_CURRENT_BINARY_DIR}/copied_file${genexvar}.cpp")
 if (HAVE_FINAL)
   target_compile_features(empty PRIVATE cxx_final)
 endif()