While thinking about C++ n3694 feature test macros I noticed we still define __GXX_EXPERIMENTAL_CXX0X__ macro in c-family/c-cppbuiltin.c. We got rid of all uses of it in libstdc++. I propose we get rid of it here too. User's shouldn't be relying on it. No?
OTOH, it may have been a proxy for __cplusplus for users for a good while. People may still be using it even if the library no longer uses it. What do folks think?
