[CGData] Clang Options (#90304)
This adds new Clang flags to support codegen (CG) data:
- `-fcodegen-data-generate{=path}`: This flag passes
`-codegen-data-generate` as a boolean to the LLVM backend, causing the
raw CG data to be emitted into a custom section. Currently, for LLD
MachO only, it also passes `--codegen-data-generate-path=<path>` so that
the indexed CG data file can be automatically produced at link time. For
linkers that do not yet support this feature, `llvm-cgdata` can be used
manually to merge this CG data in object files.
- `-fcodegen-data-use{=path}`: This flag passes
`-codegen-data-use-path=<path>` to the LLVM backend, enabling the use of
specified CG data to optimistically outline functions.
- The default `<path>` is set to `default.cgdata` when not specified.
This depends on https://github.com/llvm/llvm-project/pull/108733.
This is a patch for
https://discourse.llvm.org/t/rfc-enhanced-machine-outliner-part-2-thinlto-nolto/78753.
