__GXX_EXPERIMENTAL_CXX0X__

[Neal Becker]

I need a preprocessor macro to detect c++0x support.  For now, that is
 __GXX_EXPERIMENTAL_CXX0X__

but what happens once -std=c++0x is the default?  Will this macro still
be defined?  

Don't we need a

__GXX_CXX0X__ ?