What is the proper way to install a package under custom sub directory under LOCALBASE ?

[Yosuke Kawasaki <you.kawasaki%gmail.com@localhost>]

Hello,

I am trying to make a local pkg of AMD-forked llvm
(https://github.com/ROCm-Developer-Tools/llvm-project, version 4.1.0)
and to install it into a custom subdirectory under LOCALBASE in order
to avoid collision with files from the standard llvm package.

llvm uses CMAKE and when I set
CMAKE_INSTALL_PREFIX=LOCALBASE/sub-directory in pkg Makefile, it
installs files under LOCALBASE/sub-directory.  However, some installed
executables and libraries such as bin/llvm-link have a parameter
RUNPATH, which is  directed to "/usr/pkg/lib", instead of
"/usr/pkg/<sub-directory>/lib" and cannot find shared libraries
installed together e.g. libLLVM-12git.so.

What is the proper way to install a package under a custom subdirectory?

Best regards,

Yosuke Kawasaki