cmake: add opt-in portable RPATHs for TheRock ROCm wheels

[sa-faizal]

The default CMAKE_INSTALL_RPATH_USE_LINK_PATH policy copies build-environment ROCm library directories into installed wheel RUNPATHs. Those absolute paths do not exist in a clean installation.

Add an opt-in THEROCK_PYTORCH_PORTABLE_RPATH policy that:

• disables automatic link-directory capture;
• keeps $ORIGIN for Torch's own libraries;
• adds wheel-relative paths to _rocm_sdk_core and _rocm_sdk_libraries;
• derives the Clang resource version from the configured compiler instead of hard-coding a ROCm release.

The option defaults to OFF, so existing builds retain their current behavior. The libtorchless MKL override also respects the opt-in policy.

Validation:

• CMake tracing confirmed the portable list and CMAKE_INSTALL_RPATH_USE_LINK_PATH=FALSE when enabled.
• The disabled path retains the existing link-path policy.
• A configure run reached and reported the new policy before stopping on unrelated missing host Python packages.
• git diff --check passes.

Stacked follow-up: ROCm/TheRock#7210 enables this option for its production PyTorch wheel builder and rejects absolute wheel RPATH/RUNPATH entries before publishing artifacts.