Update paths in cmake config files provided by HIP and hipamd to the proper
location in the Nix store. Previously these files were trying to find headers
in a way that assumes the typical ROCm installation (where everything is in
/opt/rocm). This resulted in a bunch of errors when trying to compile HIP
projects that are configured with cmake, like include paths that were set
incorrectly or header paths that were not found.
This is the supported way rocm is tested.
It makes packaging in nix a *lot* easier (see the code size).
An important change is the dontLink detection in the clang/clang++
wrapper script: When compiling with --cuda-device-only,
the linker must not be set, otherwise e.g. the blender kernels fail to
compile.
