[Bug c++/67888] Compiling clang 3.7.0 results in is used but never defined

[rodrigc at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67888

--- Comment #3 from Craig Rodrigues <rodrigc at gcc dot gnu.org> ---
This is for cross-compiling the FreeBSD base system with GCC.
The FreeBSD base system has libc++, which was recently upgraded to clang 3.7.0.

Cross-compiling FreeBSD base system with GCC worked before,
with an older version of libc++.

Discussion on the llvm cfe-dev mailing list seems to point to this
being a bug in GCC, hence I filed this bug.