GNU C++: record that -fvisibility-inlines-hidden is available since 4.0

See https://gcc.gnu.org/onlinedocs/gcc-4.0.0/gcc/Option-Summary.html

Modules/Compiler/GNU-CXX.cmake

@@ -6,7 +6,7 @@ if (WIN32)
     set(CMAKE_CXX_COMPILE_OPTIONS_VISIBILITY_INLINES_HIDDEN "-fno-keep-inline-dllexport")
   endif()
 else()
-  if(NOT CMAKE_CXX_COMPILER_VERSION VERSION_LESS 4.2)
+  if(NOT CMAKE_CXX_COMPILER_VERSION VERSION_LESS 4.0)
     set(CMAKE_CXX_COMPILE_OPTIONS_VISIBILITY_INLINES_HIDDEN "-fvisibility-inlines-hidden")
   endif()
 endif()