Cygwin has exported error.h since 1.7.10.

--- origsrc/gettext-0.18.1.1/gettext-tools/libgettextpo/error.h	2010-02-16 15:33:13.000000000 -0600
+++ src/gettext-0.18.1.1/gettext-tools/libgettextpo/error.h	2013-01-24 22:19:12.749318500 -0600
@@ -49,14 +49,14 @@ extern void error_at_line (int __status,
 /* If NULL, error will flush stdout, then print on stderr the program
    name, a colon and a space.  Otherwise, error will call this
    function without parameters instead.  */
-extern DLL_VARIABLE void (*error_print_progname) (void);
+extern __declspec(dllimport) void (*error_print_progname) (void);
 
 /* This variable is incremented each time `error' is called.  */
-extern DLL_VARIABLE unsigned int error_message_count;
+extern __declspec(dllimport) unsigned int error_message_count;
 
 /* Sometimes we want to have at most one error per line.  This
    variable controls whether this mode is selected or not.  */
-extern DLL_VARIABLE int error_one_per_line;
+extern __declspec(dllimport) int error_one_per_line;
 
 #ifdef __cplusplus
 }
--- origsrc/gettext-0.18.1.1/gettext-tools/woe32dll/gettextlib-exports.c	2010-06-06 07:49:58.000000000 -0500
+++ src/gettext-0.18.1.1/gettext-tools/woe32dll/gettextlib-exports.c	2013-01-24 21:17:39.584846100 -0600
@@ -18,9 +18,6 @@
 #include "woe32dll/export.h"
 
 VARIABLE(argmatch_die)
-VARIABLE(error_message_count)
-VARIABLE(error_one_per_line)
-VARIABLE(error_print_progname)
 VARIABLE(error_with_progname)
 VARIABLE(exit_failure)
 VARIABLE(gl_array_list_implementation)