Let's look at the non-conditional C11 major changes:

>additional floating-point characteristic macros (<float.h>)

VS2015 RC.

>querying and specifying alignment of objects (<stdalign.h>, <stdlib.h>)

Missing but the functionality is available as extensions.

>Unicode characters and strings (<uchar.h>) (originally specified in ISO/IEC TR 19769:2004)

VS2015 RC.

>type-generic expressions

Missing. (Use C++ instead. trollface.dds)

>static assertions

Missing but (incorrectly) static_assert can be used instead of _Static_assert.

>anonymous structures and unions

Partially or maybe even completely. I would have to check but for trivial usage I'd consider it to be complete.

>no-return functions

Missing but __declspec(noreturn) can be used instead.

>support for opening files for exclusive access

Missing but _fsopen() / _wfsopen() and _SH_DENYRW can be used instead.

>removed the gets function (<stdio.h>)

VS2015 RC.

>added the aligned_alloc, at_quick_exit, and quick_exit functions (<stdlib.h>)

Partially as aligned_alloc() is missing.