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

[Eli Friedman via llvm-commits]

efriedma-quic wrote:

Updated with some comments, and cleaned up one of the ifdefs a bit.

My thinking for the filenames is that we actually should split InstrProfilingPlatformLinux.c: we should have InstrProfilingPlatformELF.c for the ELF-only bits, and InstrProfilingPlatformStaticInit.c for the "generic" __start/__stop bits, and InstrProfilingPlatformWasm.c for the wasm-only bits (basically just a stub, but it doesn't fit anywhere else).  Then rename InstrProfilingPlatformOther.c to InstrProfilingPlatformDynamicInit.c.  But I'd prefer to leave that for a followup.

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