Cortex-M3 vector_catch testing support

The "cm3-ftest.cfg" can be used to verify that OpenOCD handles
certain faults correctly:

 - Test #1: it ignores faults that it wasn't told to catch
 - Test #2: if vector_catch is told to catch, it catches

The "fault.c" generates ASM code to trigger faults, while the
config script loads and runs pre-compiled code.

This covers most, but not all, of the vector_catch options.

Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>