[bug-gettext] Errors building with getttext-runtime/po/Makefile.in.in

[Ed]

gettext-runtime/po/Makefile.in.in uses the variable top_builddir, but
that variable is not directly set in the makefile, unlike (for
example) top_srcdir.

This causes build errors for me building applications out-of-tree
(specifically, freedroid latest has this problem for me with autoconf
2.69, automake 1.15.1 - the latest for Ubuntu 18.04).

I think the fix is just to add

top_builddir = @top_builddir@

to the top of the file.

For me, this eliminates the build errors.

One curiosity is that everything in this file seems to be quite old,
which reduces my confidence in having identified the root of the
problem. My best guess is that autotools generated makefiles no longer
export all variables by default, and before when they did this issue
was disguised.

Anyway, I hope this is of use to someone.

Cheers

Ed