Re: Option ansi2knr mishandles sources in different directories

[Kevin Ryde]

This is also my PR/370 covered I guess.

I notice the _.c is produced in the subdirectory.  In GMP we've got a
case where we'd like to take sources from a directory which also has
its own build of the respective files, with the two builds using a
couple of different -D defines (just using the INCLUDES variable).  I
wonder if the old way of having the _.c in the current directory could
be retained.

I also notice in this change that if the subdirectory doesn't have its
own Makefile.am then the _.c isn't removed by a clean or distclean.