[patch] toplevel configure.in: topsrcdir->srcdir

[DJ Delorie]

> 'topsrcdir' always refers to the top level directory where 'configure'
> is located.  When 'configure.in' in the top directory is being run,
> srcdir is normally the same directory.  In a subdirectory, srcdir and
> topsrcdir differ, but not at the top level.

The case I'm worried about is a src=build cross.  In that case,
configure builds a whole new source tree!  So we must make sure that
it doesn't run the toplevel configure that it may copy to some other
directory, or if it does, that topsrcdir refers to the original
toplevel, not the newly copied one.

I don't think it should do this (it should only copy subdirectories)
but this is one of the cases that often goes unworking for long
periods.