[compiler-rt] [compiler-rt] Add baremetal version of profile library. (PR #167998)

[Eli Friedman via llvm-commits]

efriedma-quic wrote:

> If I've understood the scope of the change. The user/toolchain would still have to arrange for a mechanism to construct a means to output the counters in a format that llvm-profdata understands.

This subset of the profile library includes `__llvm_profile_write_buffer`, which outputs counters in the format llvm-profdata expects.  Obviously the user still needs to copy that data off the device somehow.

https://github.com/llvm/llvm-project/pull/167998