Tracking issue for LLVM 20 support.

Mesa:

• Might just work, the only PR I saw was for clover (GPU arch we don't support): https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/33805
• Looks like there's an upstream issue breaking building mesa w/ Polly (we weren't doing that anyway): clang 20.1.1/19.1.7 hangs when compiling a specific Mesa file src/mesa/main/format_utils.c for x86; compilation never finishes after 2 hours llvm/llvm-project#132717

Rust:

• Support will land in Rust 1.87.0 (due for release May 15th): Update to LLVM 20 rust-lang/rust#135763

LDC:

• Open PR, hasn't seen any activity in a few weeks: Preliminary LLVM 20 support ldc-developers/ldc#4843

qt5-tools/qt6-tools:

• Fedora rebuilt it without additional changes

spirv-llvm-translator:

• Supports it: https://github.com/KhronosGroup/SPIRV-LLVM-Translator/releases/tag/v20.1.0

linux-tools:

• Unknown

doxygen:

• Unknown