compiler: only import variable into . if same package

If we dot-import a package, we should only add an imported variable to
    the package bindings if the variable is in the package being imported.
    A test case for this is the 1.13 os package, in which ErrClosed and
    friends are defined both locally and in the imported internal/oserror package.
    
    Reviewed-on: https://go-review.googlesource.com/c/gofrontend/+/192718

From-SVN: r275358

gcc/go/gofrontend/MERGE

@@ -1,4 +1,4 @@
-3b8a505824abb2a69f4c04c555a4ba29ab8b102b
+ca0fdb4c7735a648b8f10f1248631adf9afb8454
 
 The first line of this file holds the git revision number of the last
 merge done from the gofrontend repository.

gcc/go/gofrontend/import.cc

@@ -777,7 +777,7 @@ Import::import_var()
 			       this->location_);
   Named_object* no;
   no = vpkg->add_variable(name, var);
-  if (this->add_to_globals_)
+  if (this->add_to_globals_ && vpkg == this->package_)
     this->gogo_->add_dot_import_object(no);
 }