[BUILD] Enable RCCL build with amdclang++

[nileshnegi]

Details

Work item: Internal

What were the changes?
Enable the use of amdclang++ instead of hipcc for building RCCL.

Why were the changes made?

• Update CXX and C compiler and flags in toolchain-linux.cmake
• Update CMakeLists.txt for amdclang++-related checks
• Replace hipcc --version with hipconfig -v in CMakeLists.txt to query the HIP version, as amdclang++ --version does not report HIP version

Approval Checklist

Do not approve until these items are satisfied.

• [ ] Verify the CHANGELOG has been updated, if
  • there are any NCCL API version changes,
  • any changes impact library users, and/or
  • any changes impact any other ROCm library.