Detect bug in cygwin 1.5.x *printf on 1-character %ls.

Detect bug in cygwin 1.5.x *printf on 1-character %ls.

* m4/printf.m4 (gl_PRINTF_DIRECTIVE_LS): Enhance filter.
* doc/posix-functions/fprintf.texi: Update.
* doc/posix-functions/printf.texi: Update.
* doc/posix-functions/snprintf.texi: Update.
* doc/posix-functions/sprintf.texi: Update.
* doc/posix-functions/vfprintf.texi: Update.
* doc/posix-functions/vprintf.texi: Update.
* doc/posix-functions/vsnprintf.texi: Update.
* doc/posix-functions/vsprintf.texi: Update.
* doc/glibc-functions/obstack_printf.texi: Update.
* doc/glibc-functions/obstack_vprintf.texi: Update.

Signed-off-by: Eric Blake <ebb9@byu.net>