configure.ac: Don't look for Xwayland in the weston install destination

Xwayland isn't part of this distribution so looking for Xwayland in
weston's install dir will cause distcheck to fail.  Let's set the
default to /usr/bin where it's likely to live.

It can still be overriden during configure exactly as before.

Signed-off-by: Derek Foreman <derekf@osg.samsung.com>
Reviewed-by: Daniel Stone <daniels@collabora.com>

configure.ac

@@ -100,7 +100,7 @@ if test x$enable_xwayland = xyes; then
 
   AC_ARG_WITH(xserver-path, AS_HELP_STRING([--with-xserver-path=PATH],
               [Path to X server]), [XSERVER_PATH="$withval"],
-              [XSERVER_PATH="$bindir/Xwayland"])
+              [XSERVER_PATH="/usr/bin/Xwayland"])
   AC_SUBST([XSERVER_PATH])
   if test x$enable_xwayland_test = xyes; then
     PKG_CHECK_MODULES([XWAYLAND_TEST], x11)