[compiler-rt] r202377 - Add CODE_OWNERS.TXT

I’ve added CODE_OWNERS.TXT to compiler-rt repository. You’re welcome to verify its contents and/or nominate more people. In particular, I don’t know who is currently responsible for
the “original” compiler-rt library (which now resides under lib/builtins), both its generic and platform-specific parts.

[As discussed off-line, I'll add myself as an
AddressSanitizer-for-Windows owner]