implement fdiagnostics-print-source-range-info

[Tom Tromey]

>>>>> "Manuel" == Manuel López-Ibáñez <lopezibanez@gmail.com> writes:

>> Why put struct location_range and location_t in libcpp, but
>> UNKNOWN_LOCATION_RANGE in gcc?

Manuel> You are right. I think I'll move everything in toplev.c to line-map.
Manuel> Anyway, it is not in libcpp, it is in line-map, which in turn is in
Manuel> libcpp because we cannot be bothered to move it anywhere else.

I thought about this patch a little more and I had one other comment.  I
would rather not move location_t to libcpp.  It is not part of the
libcpp API, and it isn't used by libcpp at all.  It is a GCC
implementation detail, so IMO ought to remain in GCC.

Tom