[libc++] Simplify conditional in __config for _LIBCPP_NO_RTTI

We don't support GCC's older than 5.x anymore.

Author: ldionne

libcxx/include/__config

@@ -1106,12 +1106,8 @@ _LIBCPP_FUNC_VIS extern "C" void __sanitizer_annotate_contiguous_container(
 
 // Try to find out if RTTI is disabled.
 // g++ and cl.exe have RTTI on by default and define a macro when it is.
-// g++ only defines the macro in 4.3.2 and onwards.
 #if !defined(_LIBCPP_NO_RTTI)
-#  if defined(__GNUC__) && \
-      ((__GNUC__ >= 5) || \
-       (__GNUC__ == 4 && (__GNUC_MINOR__ >= 3 || __GNUC_PATCHLEVEL__ >= 2))) && \
-      !defined(__GXX_RTTI)
+#  if defined(__GNUC__) && !defined(__GXX_RTTI)
 #    define _LIBCPP_NO_RTTI
 #  elif defined(_LIBCPP_COMPILER_MSVC) && !defined(_CPPRTTI)
 #    define _LIBCPP_NO_RTTI