Rollup merge of #95963 - luqmana:llvm-dist-cross-filecheck, r=Mark-Simulacrum

[bootstrap] Grab the right FileCheck binary for dist when cross-compiling.

Fixes #95862

We were using the target dir for all the other LLVM tools (`llvm-config`, `llvm-ar`, etc) but the build target dir for `FileCheck`. This meant for targets which are cross-compiled, we were copying the wrong binary.