[llvm] [offload] Fix finding amdgpu/nvptx-arch to generate tests (PR #135072)

[Joel E. Denny via llvm-commits]

jdenny-ornl wrote:

When I grep LLVM source for LLVM_TOOLS_BINARY_DIR, I see stuff like:

```
clang/CMakeLists.txt:  set(LLVM_TOOLS_BINARY_DIR "${LLVM_TOOLS_BINARY_DIR}" CACHE PATH "Path to llvm/bin")
clang/CMakeLists.txt:    if(EXISTS ${LLVM_TOOLS_BINARY_DIR}/FileCheck${CMAKE_EXECUTABLE_SUFFIX}
runtimes/CMakeLists.txt:  set(LLVM_TOOLS_BINARY_DIR ${LLVM_BINARY_DIR}/bin)
```

So it appears to be normal for it to include bin.  Am I missing your point?

https://github.com/llvm/llvm-project/pull/135072