Split host and device libraries

This is a feature request.

Linking libishmem.a is very slow due to device code compilation/linking.
I only intended to use the host side features.
NVSHMEM provides libnvshmem_host.so and nvshmemx_hostlib_init_attr/nvshmemx_hostlib_finalize APIs.
I'd like Intel SHMEM to match that.