Fix PTRACE_SETOPTIONS tests

Fix PTRACE_SETOPTIONS tests

* strace.c [LINUX] (kill_save_errno): New function.
(test_ptrace_setoptions_followfork): Change return type to void.
Fix and harden error handling.  Use kill_save_errno() to avoid errno
clobbering.  Treat EIO from ptrace() the same way as EINVAL.
(test_ptrace_setoptions_for_all): Use kill_save_errno() to avoid errno
clobbering.  Treat EIO from ptrace() the same way as EINVAL.
(main): Update use of test_ptrace_setoptions_followfork().