It only makes sense to use the CMake package from the same ROCm
installation that the compiler uses. Ask the HIP compiler to report the
location of the ROCm installation. Verify up front that it contains the
expected CMake package file.
Update the logic that converts a `try_compile` result from a cache
entry to a normal variable to tolerate an existing normal variable
under CMP0126 NEW behavior. Otherwise the `try_compile` result
is ignored because CMake uses the false value of the normal variable,
and CMake incorrectly reports that the compiler does not work.
This went unnoticed for some languages (e.g. C and CXX) because the
check for a working compiler is skipped if ABI detection works.
It does affect other languages (e.g. CSharp).
Fixes: #22423
