Don't expect the UDL definition for GCC < 4.9

The compile tests should expect the UDL to
be there on GCC only for version 4.9 and above.

test/compile-error-test/CMakeLists.txt

@@ -177,6 +177,12 @@ set(CMAKE_REQUIRED_FLAGS )
 if (NOT SUPPORTS_USER_DEFINED_LITERALS)
   set (SUPPORTS_USER_DEFINED_LITERALS OFF)
 endif ()
+if (SUPPORTS_USER_DEFINED_LITERALS AND CMAKE_COMPILER_IS_GNUCXX)
+  # GCC before 4.9 is not supported for user-defined literals as it requires an
+  # invalid syntax in their definition.
+  set (SUPPORTS_USER_DEFINED_LITERALS
+    $<IF:$<$<VERSION_LESS:$<CXX_COMPILER_VERSION>,4.9.0>,OFF,ON>
+endif()
 
 # Make sure that compiler features detected in the header
 # match the features detected in CMake.