[compiler-rt] [profile] Implement a non-mmap path when reading profile files from a non-local filesystem (PR #131177)

[Arthur Eubanks via llvm-commits]

aeubanks wrote:

I've reverted this PR in 32476b99344fb0a3b85acbdba666e165181ec638 due to the tests failing on mac. Feel free to reland once you've figured out what's going on there

https://github.com/llvm/llvm-project/pull/131177