Features: Fix GNU 4.8.1 version test.

Modules/Compiler/GNU-CXX-FeatureTests.cmake

@@ -3,7 +3,7 @@
 
 set(_oldestSupported "(__GNUC__ * 100 + __GNUC_MINOR__) >= 407")
 # Introduced in GCC 4.8.1
-set(GNU481_CXX11 "((__GNUC__ * 100 + __GNUC_MINOR__) >= 408 && __GNUC_PATCHLEVEL__ >= 1) && __cplusplus >= 201103L")
+set(GNU481_CXX11 "((__GNUC__ * 10000 + __GNUC_MINOR__ * 100 + __GNUC_PATCHLEVEL__) >= 40801) && __cplusplus >= 201103L")
 set(_cmake_feature_test_cxx_decltype_incomplete_return_types "${GNU481_CXX11}")
 set(_cmake_feature_test_cxx_reference_qualified_functions "${GNU481_CXX11}")
 set(GNU48_CXX11 "(__GNUC__ * 100 + __GNUC_MINOR__) >= 408 && __cplusplus >= 201103L")