[BUILD] Support custom CMake flags in MSCCLPP

[nileshnegi]

Details

Work item: Internal

What were the changes?
Support custom CMAKE_PREFIX_PATH when building MSCCLPP

Why were the changes made?
CMAKE_PREFIX_PATH specified for RCCL build was not being passed to MSCCLPP build

How was the outcome achieved?
Modify CMake command for MSCCLPP

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.