The host libLLVM.so (COOKBOOK_HOST_SYSROOT=/usr branch) lives in the redoxer
toolchain and is dynamically linked by rustc's librustc_driver. Building it as
X86;AMDGPU;NVPTX only dropped AArch64/RISCV, so after the AMDGPU splice rustc
failed to load with 'undefined symbol: LLVMInitializeAArch64AsmPrinter' —
breaking every Rust compile in the tree. Build the host LLVM with all CPU
targets rustc emits (X86;AArch64;RISCV) PLUS the GPU backends (AMDGPU;NVPTX).
The Redox-target llvm21 stays X86;AMDGPU;NVPTX (Redox is amd64-only, no need to
bloat the shipped libLLVM with foreign CPU backends).
Fixes a latent regression from 80d20db8/a6999912.
vasilito
c775ea2539