libasprintf: Add metainformation for Windows.
* gettext-runtime/libasprintf/configure.ac: Set RC and WOE32 variables.
* gettext-runtime/libasprintf/libasprintf.rc: New file.
* gettext-runtime/libasprintf/Makefile.am (EXTRA_DIST): Add it.
(WOE32_LIBADD): New variable.
(libasprintf.res.lo): New rule.
(libasprintf_la_LIBADD, libasprintf_la_DEPENDENCIES): New variables.
