RFR: 8302838: jabswitch main() should avoid calling exit explicitly [v2]

[Julian Waters]

> In jabswitch, main is defined as `void main()`, which requires an explicit exit call whenever an error occurs, and extra error checking code on our part. Visual C++ will automatically convert all instances of `void main()` to return 0 in all cases anyway, and there isn't anything gained from using this custom signature when the same can be achieved by simply returning the error value normally, so I propose we simply change it to the regular `int main` signature

Julian Waters has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains two additional commits since the last revision:

 - Merge branch 'openjdk:master' into patch-8
 - jabswitch.cpp

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Changes:
  - all: https://git.openjdk.org/jdk/pull/12650/files
  - new: https://git.openjdk.org/jdk/pull/12650/files/c5783d47..a04b8f51

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=12650&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=12650&range=00-01

  Stats: 3652 lines in 172 files changed: 2273 ins; 939 del; 440 mod
  Patch: https://git.openjdk.org/jdk/pull/12650.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/12650/head:pull/12650

PR: https://git.openjdk.org/jdk/pull/12650