compiler: preserve nointerface property when inlining methods

When an inline function (with body) is imported from another package,
    make that the "nointerface" property (if set) is preserved.
    
    Fixes golang/go#30862.
    
    Reviewed-on: https://go-review.googlesource.com/c/gofrontend/+/167742

From-SVN: r269713

gcc/go/gofrontend/MERGE

@@ -1,4 +1,4 @@
-a99959e6a4a899cfcc4d46e6b54da15d23c58a14
+cc70be24502faeffefb66fd0abeb7f20a6c7792a
 
 The first line of this file holds the git revision number of the last
 merge done from the gofrontend repository.

gcc/go/gofrontend/gogo.cc

@@ -6899,6 +6899,8 @@ Function_declaration::import_function_body(Gogo* gogo, Named_object* no)
 
   if (fntype->is_method())
     {
+      if (this->nointerface())
+        fn->set_nointerface();
       const Typed_identifier* receiver = fntype->receiver();
       Variable* recv_param = new Variable(receiver->type(), NULL, false,
 					  true, true, start_loc);