r188651 - DebugInfo: Do not include line/file info for artificial parameters & parameters of artificial functions

[Robinson, Paul]

> DebugInfo: Do not include line/file info for artificial parameters &
> parameters of artificial functions
...
> -// It's weird that the first two parameters are recorded as being in a
> -// different, ("<unknown>") file compared to the third parameter which
> is 'in'
> -// the actual source file. (see the metadata node after the arg name in
> each
> -// line)

I've seen the debug info for the artificial functions themselves also
have bogus source coordinates.  Being artificial functions, people don't
care much so I haven't pursued it.  

The .debug_line info for these guys isn't always right either.  Meaning,
the file number is obviously wrong.

But I wonder if just not emitting the source locations is papering over 
some other not-keeping-track problem.
--paulr