[PGO][Offload] Profile profraw generation for GPU instrumentation #76587  (#93365)

This pull request is the second part of an ongoing effort to extends PGO
instrumentation to GPU device code and depends on #76587. This PR makes
the following changes:

- Introduces `__llvm_write_custom_profile` to PGO compiler-rt library.
This is an external function that can be used to write profiles with
custom data to target-specific files.
- Adds `__llvm_write_custom_profile` as weak symbol to libomptarget so
that it can write the collected data to a profraw file.
- Adds `PGODump` debug flag and only displays dump when the
aforementioned flag is set

GitOrigin-RevId: 9e5c136d5a1a8acee9e7acfbe14cc6d4490dee2e
1 file changed