Cygwin: path_conv: add PC_SYM_NOFOLLOW_DIR flag

Usually a trailing slash requires to follow an existing symlink,
even with PC_SYM_NOFOLLOW.  The reason is that "foo/" is equivalent
to "foo/." so the symlink is in fact not the last path component,
"." is.  This is default for almost all scenarios.

PC_SYM_NOFOLLOW_DIR now allows the caller to request not to
follow the symlink even if a trailing slash is given.  This can
be used in callers to perform certain functions Linux-compatible.

Signed-off-by: Corinna Vinschen <corinna@vinschen.de>

winsup/cygwin/path.h

@@ -59,6 +59,7 @@ enum pathconv_arg
   PC_SYM_NOFOLLOW_PROCFD = _BIT (11),	/* allow /proc/PID/fd redirection */
   PC_KEEP_HANDLE	 = _BIT (12),	/* keep handle for later stat calls */
   PC_NO_ACCESS_CHECK	 = _BIT (13),	/* helper flag for error check */
+  PC_SYM_NOFOLLOW_DIR	 = _BIT (14),	/* don't follow a trailing slash */
   PC_DONT_USE		 = _BIT (31)	/* conversion to signed happens. */
 };