Fix the test for running the CxxDialog unit test.

The existing versions have been used since commit
v3.1.0-rc1~635^2~8 (cmTarget: Add CXX_STANDARD and CXX_EXTENSION
target properties., 2013-10-13), but further discussions since then
increased the initial minimum compiler versions this feature is
available for.

Tests/CMakeLists.txt

@@ -292,11 +292,11 @@ if(BUILD_TESTING)
   endif()
   ADD_TEST_MACRO(SourcesProperty SourcesProperty)
   if(CMAKE_CXX_COMPILER_ID STREQUAL GNU
-      AND NOT CMAKE_CXX_COMPILER_VERSION VERSION_LESS 4.6)
+      AND NOT CMAKE_CXX_COMPILER_VERSION VERSION_LESS 4.7)
     set(runCxxDialectTest 1)
   endif()
   if(CMAKE_CXX_COMPILER_ID STREQUAL Clang
-        AND NOT CMAKE_CXX_COMPILER_VERSION VERSION_LESS 2.9)
+        AND NOT CMAKE_CXX_COMPILER_VERSION VERSION_LESS 3.4)
     if(NOT APPLE OR POLICY CMP0025)
       set(runCxxDialectTest 1)
     endif()