sim: testsuite: fix cris badarch in multi-target builds

sim: testsuite: fix cris badarch in multi-target builds

This test assumes that /bin/sh will never be a CRIS ELF by way of
assuming that the current bfd cannot load it (since a basic cris
cross-compiler only understands CRIS ELFs).  In a multi-target
build though, bfd understands just about every ELF out there, so
we're able to read the /bin/sh format before failing at a diff
point in the cris code.

Let's switch to using / instead since it'll fail for a similar
reason (at least similar enough for what this test is testing).