[LLVM] Make the GPU loader utilities an LLVM tool (#132096)

Summary:
These tools `amdhsa-loader` and `nvptx-loader` are used to execute unit
tests directly on the GPU. We use this for `libc` and `libcxx` unit
tests as well as general GPU experimentation. It looks like this.

```console
> clang++ main.cpp --target=amdgcn-amd-amdhsa -mcpu=native -flto -lc ./lib/amdgcn-amd-amdhsa/crt1.o
> llvm-gpu-loader a.out
Hello World!
```

Currently these are a part of the `libc` project, but this creates
issues as `libc` itself depends on them to run tests. Right now we get
around this by force-including the `libc` project prior to running the
runtimes build so that this dependency can be built first. We should
instead just make this a simple LLVM tool so it's always available.

This has the effect of installing these by default now instead of just
when `libc` was enabled, but they should be relatively small. Right now
this only supports a 'static' configuration. That is, we locate the CUDA
and HSA dependencies at LLVM compile time. In the future we should be
able to provide this by default using `dlopen` and some API.

I don't know if it's required to reformat all of these names since they
used the `libc` naming convention so I just left it for now.