[lld] [llvm] Reapply "Use an abbrev to reduce size of VALUE_GUID records in ThinLTO summaries" (#90610) (PR #90692)

[Jan Voung via llvm-commits]

jvoung wrote:

Hi Kamau, thanks for looking into that!

Not sure of a great solution yet either, but some notes from an initial scan:
- `lld-available` depends on `config.has_lld` [link](https://github.com/llvm/llvm-project/blob/54d6f6626d9377115f3db3ab3fd5994b0de5a268/compiler-rt/test/lit.common.cfg.py#L499)
- not totally sure what controls `has_lld` but looks like it could depend on `COMPILER_RT_HAS_LLD_PYBOOL` [link](https://github.com/llvm/llvm-project/blame/54d6f6626d9377115f3db3ab3fd5994b0de5a268/compiler-rt/test/lit.common.configured.in#L40)
- `COMPILER_RT_HAS_LLD` seems to be set around [here](https://github.com/llvm/llvm-project/blob/d53425e2a33a0ff7336c86d3f668b1855c47a6de/compiler-rt/CMakeLists.txt#L785) if `LINKER_IS_LLD` or `LLVM_TOOL_LLD_BUILD`. I assume you don't have `LLVM_TOOL_LLD_BUILD`
- `LINKER_IS_LLD` can be set [at least here](https://github.com/llvm/llvm-project/blob/d53425e2a33a0ff7336c86d3f668b1855c47a6de/llvm/cmake/modules/HandleLLVMOptions.cmake#L20)

Looking at the later two locations, perhaps setting `LLVM_USE_LINKER` and/or `CMAKE_LINKER` could help control that? I'm having a bit of trouble reproducing, so I'm not sure if those are the best solutions yet, but thought I'd share for discussion.

https://github.com/llvm/llvm-project/pull/90692