compiler: Don't make void-typed temporaries.

Fixes golang/go#11568.
    
    Reviewed-on: https://go-review.googlesource.com/12653

From-SVN: r226788

gcc/go/gofrontend/MERGE

@@ -1,4 +1,4 @@
-5891a4c0615f469edcefc6d7a85a88984ba940aa
+3bd90ea170b9c9aecedd37796acdd2712b29922b
 
 The first line of this file holds the git revision number of the last
 merge done from the gofrontend repository.

gcc/go/gofrontend/statements.cc

@@ -348,7 +348,15 @@ Statement::make_variable_declaration(Named_object* var)
 Type*
 Temporary_statement::type() const
 {
-  return this->type_ != NULL ? this->type_ : this->init_->type();
+  Type* type = this->type_ != NULL ? this->type_ : this->init_->type();
+
+  // Temporary variables cannot have a void type.
+  if (type->is_void_type())
+    {
+      go_assert(saw_errors());
+      return Type::make_error_type();
+    }
+  return type;
 }
 
 // Traversal.