Fix indefinite hang on no-mmu systems

Fix indefinite hang on no-mmu systems

The ptrace setoptions code will fork a child which goes to sleep and
expects the parent to continue on to do tests.  Unfortunately, this
does not work on no-mmu systems as fork() is actually vfork() and any
vforked children will hang the parent until it exits or execs.

We might be able to make this test work on no-mmu systems with a bit
of work, but easier to just disable this for the release so it works
now.

* strace.c (test_ptrace_setoptions_for_all): Return if strace_vforked.

Signed-off-by: Mike Frysinger <vapier@gentoo.org>