[PATCH] compiler_rt: add low level versions of profile buffer functions.

[Justin Bogner]

larry at elder-gods.org writes:
> On Darwin, compiler_rt uses magic linker symbols to find the profile
> counters in the __DATA segment.  This is a reasonable method for
> normal, hosted, userspace programs.  However programs with custom
> memory layouts, such as the kernel, will need to tell compiler_rt
> explicitly where to find these sections.

This looks great, thanks! I've committed it for you with some minor
formatting cleanup in r223840.