PATCH: get --enable-mapped-location building

[Ben Elliston]

> >Seems to me that you should just use the USE_MAPPED_LOCATION code
> >unconditionally, and remove the other code.
> 
> That certainly would be more elegant, robust, and forwards-looking.
> Ben, would you mind testing that?

Tested with a bootstrap on i686-pc-linux-gnu, no regressions.
Committed.

Thanks!
Ben