[llvm-branch-commits] [LTO] Support enabling AllocToken instrumentation in backend (PR #169358)

[Marco Elver via llvm-branch-commits]

https://github.com/melver created https://github.com/llvm/llvm-project/pull/169358

Add support for running `AllocTokenPass` during the LTO backend phase,
controlled by a new internal option `-lto-alloc-token-mode`.

This is required to support running the pass after other heap allocation
optimizations (such as PGHO) in the LTO backend, avoiding interference
between them.

https://github.com/llvm/llvm-project/pull/169244