RFR: JDK-8266877: Missing local debug information when debugging JEP-330

[Jaroslav Tulach]

I am polishing support for [JEP-330](https://openjdk.java.net/jeps/330) in NetBeans ([PR-2938](https://github.com/apache/netbeans/pull/2938)) and I have problems with debugging. Local variables aren't visible as the compiler doesn't pass `-g` option when compiling the main class. I'd like to see 

![obrazek](https://user-images.githubusercontent.com/26887752/117578440-a876e000-b0ee-11eb-85b6-3c998f71879f.png)

however, that requires one to pass `-g` option to the compiler somehow. As far as I can say there is no such way and hence I decided to create this pull request. If I invoke:

$ java -agentlib:jdwp=transport=dt_socket,address=8000,server=y,suspend=y x.java

it detects JDWP is on and adds `-g` to the compiler arguments. Is this an acceptable improvement? The alternative is to avoid using JEP-330 when debugging and rather generate `.class` by invoking `javac` and then run it as usual, but I'd rather rely on JEP-330 and avoid creation of the `.class` file.

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Commit messages:
 - Recognizing also -Xrunjdwp: option
 - When jdwp agentlib is on, compile JEP-330's main class with -g option

Changes: https://git.openjdk.java.net/jdk/pull/3939/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=3939&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8266877
  Stats: 3 lines in 1 file changed: 3 ins; 0 del; 0 mod
  Patch: https://git.openjdk.java.net/jdk/pull/3939.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/3939/head:pull/3939

PR: https://git.openjdk.java.net/jdk/pull/3939