[Linux] Test config script: Add the X11 library search path if it is not empty

If ac_x_libraries is empty it means that the library's found in the default path,
so we skip adding it to the XLIB variable as it screws up the search path.

test/configure

@@ -3794,7 +3794,11 @@ if test x$have_x = xyes; then
         :
     else
         XPATH="-L$ac_x_libraries"
-        XLIB="-lX11"
+        if test "x$ac_x_libraries" = x; then
+            XLIB="-lX11"
+        else
+            XLIB="-L$ac_x_libraries -lX11"
+        fi
     fi
 fi
 

test/configure.in

@@ -100,7 +100,11 @@ if test x$have_x = xyes; then
         :
     else
         XPATH="-L$ac_x_libraries"
-        XLIB="-lX11"
+        if test "x$ac_x_libraries" = x; then
+            XLIB="-lX11"
+        else
+            XLIB="-L$ac_x_libraries -lX11"
+        fi
     fi
 fi