configure: add helper for setting xserver directory

With this the X server directory can become independent from the
installation prefix set by autoconf.

Signed-off-by: Tiago Vignatti <tiago.vignatti@intel.com>

compositor/Makefile.am

@@ -3,7 +3,7 @@ bin_PROGRAMS = wayland-compositor
 AM_CPPFLAGS =					\
 	-DDATADIR='"$(datadir)"'		\
 	-DMODULEDIR='"$(moduledir)"'		\
-	-DBINDIR='"$(bindir)"'			\
+	-DXSERVER_PATH='"@XSERVER_PATH@"'	\
 	$(COMPOSITOR_CFLAGS)
 
 wayland_compositor_LDFLAGS = -export-dynamic

compositor/xserver-launcher.c

@@ -501,8 +501,8 @@ wlsc_xserver_handle_event(int listen_fd, uint32_t mask, void *data)
 		snprintf(logfile, sizeof logfile,
 			 "/tmp/x-log-%d", mxs->display);
 
-		if (execl(BINDIR "/Xorg",
+		if (execl(XSERVER_PATH,
-			  BINDIR "/Xorg",
+			  XSERVER_PATH,
 			  display,
 			  "-wayland",
 			  "-rootless",

configure.ac

@@ -37,6 +37,11 @@ AM_CONDITIONAL(ENABLE_XSERVER_LAUNCHER, test x$enable_xserver_launcher == xyes)
 if test x$enable_xserver_launcher == xyes; then
   PKG_CHECK_MODULES([XSERVER_LAUNCHER], xcb)
   AC_DEFINE([BUILD_XSERVER_LAUNCHER], [1], [Build the X server launcher])
+
+  AC_ARG_WITH(xserver-path, AS_HELP_STRING([--with-xserver-path=PATH],
+              [Path to X server]), [XSERVER_PATH="$withval"],
+              [XSERVER_PATH="$bindir/Xorg"])
+  AC_SUBST([XSERVER_PATH])
 fi