Clang support for Annex F (IEEE-754 / IEC 559 ) of C99/C11 ?

Hi,

I was glancing over Annex F of the C11 spec today and I was curious if
the macro `__STDC_IEC_559__` indicating compliance is defined.

There is an open bug [1] about this. Richard Smith back in 2013 said
[2] (in a related bug) that Clang does not support Annex F. Is that
still true?

It seems with Clang (3.9) on Linux with glibc 2.24 that the
`__STDC_IEC_559__` macro is defined by glibc itself by
`/usr/include/stdc-predef.h` (gets included by clang if a glibc header
gets included like `stdio.h`).

This interaction with glibc seems like a bug so I've created a bug
report [3]. Even though the bug is in glibc itself we need to come up
with a way to communicate clang's support for Annex F to glibc.

[1] https://llvm.org/bugs/show_bug.cgi?id=17005
[2] https://llvm.org/bugs/show_bug.cgi?format=multiple&id=17000
[3] https://llvm.org/bugs/show_bug.cgi?id=31653

Thanks,
Dan