[Issue 19172] Improve betterC assertion error mesage for switch_error

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=19172

Richard Cattermole <alphaglosined at gmail.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |alphaglosined at gmail.com

--- Comment #2 from Richard Cattermole <alphaglosined at gmail.com> ---
The problem will be that the file and line arguments would have been ignored.

I.e.

"No appropriate switch clause found on $FILE:$LINE" would be better than just
an assert with the message "No appropriate switch clause found".

--