https://bugs.webkit.org/show_bug.cgi?id=120896

Reviewed by Anders Carlsson.

The GTK port currently only permits using the libstdc++ standard library when compiling with
Clang. After r155143, build failures are occurring when using Clang and libstdc++ that predates
the 4.8.0 release due to the use of std::is_trivially_destructible that isn't available in
libstdc++ < 4.8.0.

To not add additional special casing, the GTK port should move onto requiring libstdc++ >= 4.8.1
when compiling with the Clang compiler. Version 4.8.1 was chosen since it's C++11 feature-complete.
This strict requirement is possible as compiling the GTK port with the Clang compiler is not really
widespread, so we can afford to adjust the required dependencies to match other ports' progression
instead of modifying the code.

* Source/autotools/CheckSystemAndBasicDependencies.m4: If the detected compiler is Clang, also check
that the libstdc++ standard library is used by testing for the __GLIBCXX__ macro that should be defined
to the value lesser than the '20130531', the date stamp used by the 4.8.1 release of libstdc++. Since
possible future releases of the 4.6 or 4.7 series of libstdc++ will also match this check due to a newer
date stamp contained in __GLIBCXX__, the std::is_trivially_destructible struct is also used so the
compilation will fail if the libstdc++ that's used is older than allowed (and therefor does not support
the feature). If the check fails, a fatal error is thrown, describing the requirement. Everything carries
on as normal otherwise.


git-svn-id: http://svn.webkit.org/repository/webkit/trunk@155246 268f45cc-cd09-0410-ab3c-d52691b4dbfc