gdb/testsuite: make runto always emit a FAIL on internal error

gdb/testsuite: make runto always emit a FAIL on internal error

I noticed that when a test uses `runto_main` and a GDB internal error
happens while running to main, no error or fail is emitted.  This is
because `runto_main` uses the `no-message` option of `runto`.

As a result, if a test fails to run to main and exits, no sign that
something went wrong is emitted.  For example, add this always-false
assertion to compute_frame_id:

    --- a/gdb/frame.c
    +++ b/gdb/frame.c
    @@ -545,6 +545,7 @@ static void
     compute_frame_id (struct frame_info *fi)
     {
       gdb_assert (!fi->this_id.p);
    +  gdb_assert (false);

       if (frame_debug)
         fprintf_unfiltered (gdb_stdlog, "{ compute_frame_id (fi=%d) ",

... and run gdb.dwarf2/dw2-align.exp.  No fail or sign that something
went wrong is shown.  It just appears as if the test gets skipped.

A developer introducing such a regression in this test today would
likely notice it, because we are used to diff-ing test results.  So we
would see some PASSes dispappear for no good reason and look into it.

But I find it worrysome for two reasons:

1. Scripts that analyze regressions (such as the one on the buildbot)
   may only look for new FAILs or new ERRORs.  It would probably miss
   this.
2. Imagine that we one day have a testsuite that runs cleanly (some
   people might already run subsets of the testsuite and expect it to
   all pass), we would just run the testsuite and check that there are
   no fails.  It would be easy to miss something like this.

In case of internal error, I suggest making `runto` emit a FAIL even if
`no-message` was passed.  This is different from other failure modes
that might be expected (whchi rightfully cause the test to simply be
skipped).  An internal error is always bad, so if it happens it should
noisily fail.

gdb/testsuite/ChangeLog:

	* lib/gdb.exp (runto): Always emit fail on internal error.

Change-Id: I6e6faed4868ea821541a23042b2d01c30058b0d3