Handle NULL in gcc_jit_context_set_str_option

gcc/jit/ChangeLog:
	* jit-recording.c (gcc::jit::recording::context::set_str_option):
	Handle NULL.

From-SVN: r218969

gcc/jit/ChangeLog

+2014-12-19  David Malcolm  <dmalcolm@redhat.com>
+
+	* jit-recording.c (gcc::jit::recording::context::set_str_option):
+	Handle NULL.
+
 2014-12-11  David Malcolm  <dmalcolm@redhat.com>
 
 	* docs/cp/topics/contexts.rst (gccjit::context::set_str_option):

gcc/jit/jit-recording.c

@@ -831,7 +831,7 @@ recording::context::set_str_option (enum gcc_jit_str_option opt,
       return;
     }
   free (m_str_options[opt]);
-  m_str_options[opt] = xstrdup (value);
+  m_str_options[opt] = value ? xstrdup (value) : NULL;
 }
 
 /* Set the given integer option for this context, or add an error if