[flang] Fix .mod file for symbols with same name as generic

When a generic has the same name as a module procedure or derived type,
the latter weren't being written to the `.mod` file. Fix that by calling
`PutSymbol()` on those symbols from the generic. Change `PutSymbol()` to
accept `Symbol *` to make that more convenient.

Original-commit: flang-compiler/f18@1778efe981812b1d1d1b684647c72085f44c3209
Reviewed-on: https://github.com/flang-compiler/f18/pull/305
Tree-same-pre-rewrite: false