Consolidate __assert_failed into one implementation

We had two implementations of __assert_failed which were almost identical,
combine them into one.

Signed-off-by: Alex Kiernan <alex.kiernan@gmail.com>

lib/panic.c

@@ -45,3 +45,11 @@ void panic(const char *fmt, ...)
 #endif
 	panic_finish();
 }
+
+void __assert_fail(const char *assertion, const char *file, unsigned int line,
+		   const char *function)
+{
+	/* This will not return */
+	panic("%s:%u: %s: Assertion `%s' failed.", file, line, function,
+	      assertion);
+}