[foreign] RFR: 8224013: jextract failed to generate source file under some scenarios

[Henry Jen]

Hi,

Please review a trivial fix[1] for 8224013[2],

jextract throws exceptions when use --src-dump-dir under following scenarios, 

1. Not specifying target package name with -t. This will cause jextract trying to write static forwarder source into root folder. 
2. If the --src-dump-dir specified is a symbolic link to an existing folder, jextract will fail with java.nio.file.FileAlreadyExistsException

Cheers,
Henry

[1] http://cr.openjdk.java.net/~henryjen/panama/8224013/webrev/
[2] https://bugs.openjdk.java.net/browse/JDK-8224013