jit: on OS X, add -Wl,-undefined,dynamic_lookup to driver invocation

gcc/jit/ChangeLog:
	* jit-playback.c (invoke_driver): On OS X, add
	"-Wl,-undefined,dynamic_lookup" to the driver arguments.

From-SVN: r226882

gcc/jit/ChangeLog

+2015-08-13  David Malcolm  <dmalcolm@redhat.com>
+
+	* jit-playback.c (invoke_driver): On OS X, add
+	"-Wl,-undefined,dynamic_lookup" to the driver arguments.
+
 2015-08-03  David Malcolm  <dmalcolm@redhat.com>
 
 	* docs/topics/compatibility.rst (LIBGCCJIT_ABI_4): New.

gcc/jit/jit-playback.c

@@ -2416,6 +2416,15 @@ invoke_driver (const char *ctxt_progname,
      time.  */
   ADD_ARG ("-fno-use-linker-plugin");
 
+#if defined (DARWIN_X86) || defined (DARWIN_PPC)
+  /* OS X's linker defaults to treating undefined symbols as errors.
+     If the context has any imported functions or globals they will be
+     undefined until the .so is dynamically-linked into the process.
+     Ensure that the driver passes in "-undefined dynamic_lookup" to the
+     linker.  */
+  ADD_ARG ("-Wl,-undefined,dynamic_lookup");
+#endif
+
   /* pex argv arrays are NULL-terminated.  */
   argvec.safe_push (NULL);