[bug-gettext] build error on Cygwin >= 1.7.10-1

[Daiki Ueno]

Hi Bruno and Windows experts,

Since 1.7.10-1, Cygwin now defines error, error_at_line,
error_message_count, error_one_per_line, error_print_progname in its DLL:
http://cygwin.com/ml/cygwin-announce/2012-02/msg00008.html

This causes the following error:
http://lists.gnu.org/archive/html/bug-gettext/2012-06/msg00007.html

Maybe gnulib could prepend "rpl_" prefix to those symbols to avoid
conflicts?

Unfortunately, even if this is fixed, the build still fails in
libgettextpo, because:

- libgettextpo does not link to gnulib's error.c anymore (because
  configure detects error_at_line)
  -> we can't use gnulib's error* variables

- when building libgettextpo, all DLL_VARIABLE are undefined
  -> we can't use Cygwin's error* variables

So we could either do:

1. use gnulib's error* variables
   i.e. link libgettextpo to gnulib's error.c
2. use Cygwin's error* variables
   i.e. do not remove "dllspec(dllimport)" attribute from error* variables

Which does sound better?  I've read the Woe32 DLL note[1] and I feel 1
might be safer.

Anyway I'll add workaround for 0.18.2 in either way.

Regards,

Footnotes: 
[1]  http://www.haible.de/bruno/woe32dll.html

-- 
Daiki Ueno