global option for clang's c++ std library?

[Titus von Boxberg]

Hi,

for those developers that use clang++ together with libc++
it would be useful to decide globally which C++ std library to use,
by adding -stdlib=libc++ to cxxflags and ldflags.

To give an example:
I'd like to use the cppunit library port. Since all of my software uses libc++
I need to compile also this library with -stdlib=libc++.

Would it make sense to add such an option globally?
Where should it be defined?
Or should such an option be introduced to every port file where it makes sense?

Adding this option globally would have the advantage that it's easy to
test already now the upcoming C++ standard library for every C++ port.
I'd expect that GNU's libstdc++ eventually will be dropped, at least the headers;
and Apple's gcc-4.2 distribution is unusable for C++11, anyway.

Regards
Titus