[gdb/testsuite] Fix gdb.base/infcall-failure.exp on freebsd

[gdb/testsuite] Fix gdb.base/infcall-failure.exp on freebsd

On x86_64-freebsd with test-case gdb.base/infcall-failure.exp I get:
...
(gdb) continue
Continuing.

Program received signal SIGSEGV, Segmentation fault.
Address not mapped to object.
0x0000000000400522 in func_segfault () at infcall-failure.c:24
24	  return *p;	/* Segfault here.  */
Error in testing condition for breakpoint 2:
The program being debugged was signaled while in a function called from GDB.
GDB remains in the frame where the signal was received.
To change this behavior use "set unwind-on-signal on".
Evaluation of the expression containing the function
(func_segfault) will be abandoned.
When the function is done executing, GDB will silently stop.
(gdb) FAIL: $exp: target_async=on: target_non_stop=on: \
  run_cond_hits_segfault_test: continue
...

The problem is that the regexp in the test-case doesn't expect the
"Address not mapped to object." bit.

Fix this by updating the regexp.

Approved-by: Kevin Buettner <kevinb@redhat.com>
Tested on x86_64-freebsd and x86_64-linux.