[Libomptarget] Reintroduce host architecture checks for device RTL

A previous patch removed the need to set the auxiliary architecture as
it was no longer needed for the clang invocation after moving to using
the clang frontend. However, this had a second use of preventing
unsupported host architectures from building the device runtime. This
caused failures when trying to build on 32-bit hosts for example.

Fixes #56699

Reviewed By: tianshilei1992

Differential Revision: https://reviews.llvm.org/D130509