glcore: prepare for dynamic loading

glcore gets linked with -ldl, -lpthread for s3tc and glapi
xserver needs
        DLOPEN_LIBS - to dlopen the glcore dso
        LD_EXPORT_SYMBOLS_FLAG - to export symbols for glcore to use

the ld flag is added to kdrive only when GLX is enabled, the net overhead for
Xephyr is ~155KB, could be reduced with --dynamic-list.

configure.ac

@@ -848,6 +848,7 @@ if test "x$GLX" = xyes && ! test "x$MESA_SOURCE" = x; then
 	if test $? -ne 0; then
 		AC_MSG_ERROR([Failed to link Mesa source tree.  Please specify a proper path to Mesa sources, or disable GLX.])
 	fi
+	GLX_SYS_LIBS="$GLX_SYS_LIBS $DLOPEN_LIBS"
 else
         GLX=no
 fi
@@ -1969,7 +1970,7 @@ if test "$KDRIVE" = yes; then
     KDRIVE_LOCAL_LIBS="$DIX_LIB $KDRIVE_LIB $KDRIVE_STUB_LIB $CONFIG_LIB"
     KDRIVE_LOCAL_LIBS="$KDRIVE_LOCAL_LIBS $FB_LIB $MI_LIB $KDRIVE_PURE_LIBS"
     KDRIVE_LOCAL_LIBS="$KDRIVE_LOCAL_LIBS $KDRIVE_OS_LIB $OS_LIB"
-    KDRIVE_LIBS="$TSLIB_LIBS $KDRIVE_LOCAL_LIBS $XSERVER_SYS_LIBS"
+    KDRIVE_LIBS="$TSLIB_LIBS $KDRIVE_LOCAL_LIBS $XSERVER_SYS_LIBS $GLX_SYS_LIBS"
 
     # check if we can build Xephyr
     PKG_CHECK_MODULES(XEPHYR, $XEPHYR_REQUIRED_LIBS, [xephyr="yes"], [xephyr="no"])