unit-tests: Change how hashtable for testable functions is created

Because GCC does not adhere to the priorities defined for constructors
when building with --enable-monolithic (not sure if it was just luck
that it worked in non-monolithic mode - anyway, it's not very portable)
function registration would fail because the hashtable would not be
created yet.

src/libstrongswan/tests/test_runner.c

@@ -32,26 +32,30 @@
 #define TTY(color) tty_escape_get(2, TTY_FG_##color)
 
 /**
- * Initialize the lookup table for testable functions (defined in libstrongswan)
+ * Initialize the lookup table for testable functions (defined in
+ * libstrongswan).  We don't use the constructor attribute as the order can't
+ * really be defined (clang does not support it and gcc does not adhere to it in
+ * the monolithic build).  The function here is a weak symbol in libstrongswan.
  */
-static void testable_functions_create() __attribute__ ((constructor(1000)));
-static void testable_functions_create()
+void testable_functions_create()
 {
-	testable_functions = hashtable_create(hashtable_hash_str,
-										  hashtable_equals_str, 8);
+	if (!testable_functions)
+	{
+		testable_functions = hashtable_create(hashtable_hash_str,
+											  hashtable_equals_str, 8);
+	}
 }
 
 /**
  * Destroy the lookup table for testable functions
  */
-static void testable_functions_destroy() __attribute__ ((destructor(1000)));
+static void testable_functions_destroy() __attribute__ ((destructor));
 static void testable_functions_destroy()
 {
-	testable_functions->destroy(testable_functions);
+	DESTROY_IF(testable_functions);
 	/* if leak detective is enabled plugins are not actually unloaded, which
 	 * means their destructor is called AFTER this one when the process
-	 * terminates, even though the priority says differently, make sure this
-	 * does not crash */
+	 * terminates, make sure this does not crash */
 	testable_functions = NULL;
 }