LLVM bootstrap builtins

[vchuravy]

[vchuravy]

Not ready yet, but I made progress on convincing cmake that this is a good idea.

https://github.com/llvm/llvm-project/blob/f4e554180962aa6bc93678898b6933ea712bde50/clang/cmake/caches/Fuchsia-stage2.cmake#L97 makes me a bit nervous

[vchuravy]

Needs https://github.com/JuliaPackaging/BinaryBuilderBase.jl/pull/34

But otherwise build builtins for many platforms.

[giordano]

For the record, there are many reasons why it'd be great to get this done eventually. Among them:

• this will probably make it possible to do LTO (link-time optimisation) when we build with clang, not possible at the moment
• it'd make LLVMCompilerRT_jll redundant
• it'd probably be a bit easier to get LLVM OpenMP instead of using LLVMOpenMP_jll
• flang has a static runtime library (similar to compiler-rt). On the one hand this lets us avoid the libgfortran explosion, on the other hand... well, we need that library built for all targets!

[ararslan]

For the record, there are many reasons why it'd be great to get this done eventually. Among them: [...]

Adding https://github.com/JuliaPackaging/Yggdrasil/pull/3540 to the list 😄

[giordano]

Adding #3540 to the list :smile:

But that was for LLVM (a regular JLL package), not the LLVMBootstrap we use for building packages, right?

[ararslan]

IIUC, including libunwind, libcxx, and libcxxabi as part of the LLVM bootstrap build would make things^{[what things?]} easier.^{[citation needed]} But the probability associated with "IIUC" is roughly 0.5.