[flang] Handle VOLATILE or ASYNCHRONOUS added to use-associated entity

When a symbol is use-associated, the VOLATILE and ASYNCHRONOUS
attributes can be added. When that happens it must be recorded
in the .mod file.

Original-commit: flang-compiler/f18@44fa9e5ba4172f75abe4194e7f58b26a99646cdc
Reviewed-on: https://github.com/flang-compiler/f18/pull/126