Use correctly-typed external definition for the crash data region, and
eliminate unnecessary pointer indirection.

Results in a small ROM saving even with crash capture disabled, as there
was a pointer for the fault context store in either case. The pointer
isn't needed, as the context store location is fixed according to the
configuration flag.

Fault handler assembly was very simplistic. Optimise for a 112 byte saving.

Tidy up formatting, and make all 3 toolchain versions more consistent,
for ease of diffing and transferring changes between them.