sim: erc32: link sis to run program

sim: erc32: link sis to run program

The erc32 sim does a lot itself, including handling of the CLI.  It
used to provide a run-compatible interface in the pre-nrun days, but
it was dropped when the old run interface was punted.  Since the old
commit 465fb143c87076b6416a8d0d5dd79bb016060fe3 ("sim: make nrun the
default run program"), the erc32 run & sis programs have been the
same, and erc32 hasn't provide a real run-compatible interface.

Simplify this by linking the two programs via ln/cp instead of running
the linking phase twice to produce the same result.  If/when we fix up
the erc32 port to have a proper run interface, it should be easy to
split these back apart into real programs.

Note: the interf.o reference in here is a bit of a misdirect.  Since
that object is placed into libsim.a, it's never been linked into the
programs since the linker ignores objects that aren't referenced, and
only gdb uses those symbols.