RFR: Naive fix for enforced dot.suffix

[Jiří Vaněk]

Afaik the ATT_SourceFile have no real impact. In dissassembeld code it differs:
```  }
} // end Class Tool compiled from "g"


  }
} // end Class Tool compiled from "g.jasm"

```  
  }
} // end Class Tool compiled from "stdin"


for imput files of g, g.jasm and stdin stream

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Commit messages:
 - Naive fix for enforced dot.suffix

Changes: https://git.openjdk.org/asmtools/pull/37/files
 Webrev: https://webrevs.openjdk.org/?repo=asmtools&pr=37&range=00
  Stats: 2 lines in 2 files changed: 0 ins; 0 del; 2 mod
  Patch: https://git.openjdk.org/asmtools/pull/37.diff
  Fetch: git fetch https://git.openjdk.org/asmtools pull/37/head:pull/37

PR: https://git.openjdk.org/asmtools/pull/37