Remove HIP_COMPILER STREQUAL "clang"

[frobnitzem]

When using the amdclang compiler through a wrapper script called "clang", HIP's cmake throws an error because it cannot find libclang_rt.builtins.

I think the source of the error is in a combination of:
https://github.com/ROCm-Developer-Tools/hipamd/blob/develop/hip-config.cmake.in
and https://github.com/ROCm-Developer-Tools/HIP/blob/develop/hip-lang-config.cmake.in

The reason that I am unsure is that the error is coming from this file in my system:
/opt/rocm-5.4.0/lib/cmake/hip/hip-config.cmake

It contains both

if(HIP_COMPILER STREQUAL "clang")
  if(WIN32)

and, later in the same file,

  file(GLOB HIP_CLANGRT_LIB_SEARCH_PATHS "${HIP_CLANG_ROOT}/lib/clang/*/lib/*")
  find_library(CLANGRT_BUILTINS
    NAMES
      clang_rt.builtins
      clang_rt.builtins-x86_64
    PATHS
      ${HIP_CLANGRT_LIB_SEARCH_PATHS}
      ${HIP_CLANG_INCLUDE_PATH}/../lib/linux
      ${HIP_CLANG_INCLUDE_PATH}/../lib/windows
      NO_DEFAULT_PATH)

The actual path to the library it's looking for on my system is
/opt/rocm-5.4.0/llvm/lib/clang/15.0.0/lib/linux/libclang_rt.builtins-x86_64.a

IMHO, resolving this issue properly requires defining and enforcing a consistent convention for rocm, llvm, and clang paths. These paths are a recurring issue in many components of rocm. A consistent convention stands to fix a lot of related troubles.