[llvm-branch-commits] [Clang][CodeGen] Move AllocToken pass to backend LTO phases (PR #169360)

[Marco Elver via llvm-branch-commits]

https://github.com/melver created https://github.com/llvm/llvm-project/pull/169360

With LTO enabled, move `AllocTokenPass` from the pre-link phase to the
backend LTO phase to avoid interference with other optimizations (e.g.
PGHO) and enable late heap-allocation optimizations.

For FullLTO and normal ThinLTO, pass AllocToken options to the linker
plugin.

For distributed ThinLTO, we need a new `PassBuilderCallback` in
`lto::Config` to inject passes into the LTO backend pipeline when
running in Clang.