RFR: 7016187: `javac -h` could generate conflict .h for inner class and class name with '_'

[Archie L. Cobbs]

Consider these two classes:

public class Foo_Bar {
    public static native void method();
}


public class Foo {
    public static class Bar {
        public static native void method();
    }
}

If you run `javac -h` to generate native header files, classes `Foo_Bar` and `Foo$Bar` will want to generate the same native header file `Foo_Bar.h`.

Currently, javac does not detect this situation, so in effect you get a "last writer wins" situation.

This patch causes compilation to fail instead in this case with an error like this:

Foo.java:2: error: error while writing Bar: native header file collision between Foo_Bar and Foo$Bar (both generate Foo_Bar.h)
    public static class Bar {
                  ^
1 error

-------------

Commit messages:
 - Fail "-h" compilation if two classes generate the same native header file.

Changes: https://git.openjdk.org/jdk/pull/12602/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=12602&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-7016187
  Stats: 42 lines in 2 files changed: 38 ins; 0 del; 4 mod
  Patch: https://git.openjdk.org/jdk/pull/12602.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/12602/head:pull/12602

PR: https://git.openjdk.org/jdk/pull/12602