Fail the build unless libSDL is installed.

diff -r a7b2638827fa -r be004ea3a553 tools/check/check_sdl_lib
@@ -0,0 +1,10 @@
+#!/bin/bash
+# CHECK-BUILD CHECK-INSTALL
+
+function error {
+        echo 'Check for SDL library failed.'
+        exit 1
+}
+
+set -e
+ldconfig -p | grep libSDL-.*so || error