`rust-lld` is no longer distributed if you link against a custom LLVM

[szilardszaloki]

rust-lld is no longer distributed as part of the package if you link against a custom LLVM (which is exactly what Chromium/Brave does), since bootstrap knows nothing about the lld that comes from the external LLVM. Raised an issue here, where the team confirmed that prior to this change, their bootstrap process unintentionally copied lld from the external location (specified by llvm-config) into the sysroot, renaming it as rust-lld.

We'll continue to use lld as rust-lld from src/third_party/rust-toolchain-intermediate/llvm-host-install/bin.