[llvm] Reapply "RuntimeLibcalls: Use get_host_tool_path for executables used … (#159488) (PR #159489)

[Martin Storsjö via llvm-commits]

mstorsjo wrote:

What issue did this attempt to fix by adding the `TARGET` checks?

If building in a configuration with e.g. `-DLLVM_NATIVE_TOOL_DIR=<dir>`, `get_host_tool_path` can find the existing binaries from there and decide that they don't need to be rebuilt - in this case, it seems like the `llvm_nm_target` and `llc_target` variables end up expanding to nothing; this then breaks the `TARGET` checks like this:

```
CMake Error at benchmarks/CMakeLists.txt:23 (if):
  if given arguments:

    "TARGET" "AND" "TARGET"

  Unknown arguments specified

```

I guess this would require a check to see that the variables expand to something non-empty as well. Or was that what the `TARGET` check tried to do in the first place?

https://github.com/llvm/llvm-project/pull/159489