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/utils/test.c

@@ -22,29 +22,46 @@
  */
 hashtable_t *testable_functions;
 
+/**
+ * The function that actually initializes the hash table above.  Provided
+ * by the test runner.
+ */
+void testable_functions_create() __attribute__((weak));
+
 /*
  * Described in header.
  */
 void testable_function_register(char *name, void *fn)
 {
-	if (testable_functions)
+	bool old = FALSE;
+
+	if (!testable_functions_create)
+	{	/* not linked to the test runner */
+		return;
+	}
+	else if (!fn && !testable_functions)
+	{	/* ignore as testable_functions has already been destroyed */
+		return;
+	}
+
+	if (lib && lib->leak_detective)
 	{
-		bool old = FALSE;
-		if (lib->leak_detective)
-		{
-			old = lib->leak_detective->set_state(lib->leak_detective, FALSE);
-		}
-		if (fn)
-		{
-			testable_functions->put(testable_functions, name, fn);
-		}
-		else
-		{
-			testable_functions->remove(testable_functions, name);
-		}
-		if (lib->leak_detective)
-		{
-			lib->leak_detective->set_state(lib->leak_detective, old);
-		}
+		old = lib->leak_detective->set_state(lib->leak_detective, FALSE);
+	}
+	if (!testable_functions)
+	{
+		testable_functions_create();
+	}
+	if (fn)
+	{
+		testable_functions->put(testable_functions, name, fn);
+	}
+	else
+	{
+		testable_functions->remove(testable_functions, name);
+	}
+	if (lib && lib->leak_detective)
+	{
+		lib->leak_detective->set_state(lib->leak_detective, old);
 	}
 }

src/libstrongswan/utils/test.h

@@ -51,7 +51,7 @@ void testable_function_register(char *name, void *fn);
  * @param fn		function to register
  */
 #define EXPORT_FUNCTION_FOR_TESTS(ns, fn) \
-static void testable_function_register_##fn() __attribute__ ((constructor(2000))); \
+static void testable_function_register_##fn() __attribute__ ((constructor)); \
 static void testable_function_register_##fn() \
 { \
 	testable_function_register(#ns "/" #fn, fn); \