RFR: 8293422: DWARF emitted by Clang cannot be parsed [v7]

[Christian Hagedorn]

> The DWARF debugging symbols emitted by Clang is different from what GCC is emitting. While GCC produces a complete `.debug_aranges` section (which is required in the DWARF parser), Clang does not. As a result, the DWARF parser cannot find the necessary information to proceed and create the line number information:
> 
> The `.debug_aranges` section contains address range to compilation unit offset mappings. The parsing algorithm can just walk through all these entries to find the correct address range that contains the library offset of the current pc. This gives us the compilation unit offset into the `.debug_info` section from where we can proceed to parse the line number information.
> 
> Without a complete `.debug_aranges` section, we fail with an assertion that we could not find the correct entry. Since [JDK-8293402](https://bugs.openjdk.org/browse/JDK-8293402), we will still get the complete stack trace at least. Nevertheless, we should still fix this assertion failure of course. But that would require a different parsing approach. We need to parse the entire `.debug_info` section instead to get to the correct compilation unit. This, however, would require a lot more work. 
> 
> I therefore suggest to disable DWARF parsing for Clang for now and file an RFE to support Clang in the future with a different parsing approach. I'm using the `__clang__` `ifdef` to bail out in `get_source_info()` and disable the `gtests`. I've noticed that we are currently running the `gtests` with `NOT PRODUCT` which I think is not necessary - the gtests should also work fine with product builds. I've corrected this as well but that could also be done separately.
> 
> Thanks,
> Christian

Christian Hagedorn has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains 10 commits:

 - Merge branch 'master' into JDK-8293422
 - Remove unused local variable
 - Update algorithm to print char by char, skipping file separators on the fly and only caring about the actual filename (ignore prefix path when reading)
 - Merge branch 'master' into JDK-8293422
 - Always read full filename and strip prefix path and only then cut filename to fit output buffer
 - Merge branch 'master' into JDK-8293422
 - Merge branch 'master' into JDK-8293422
 - Review comments from Thomas
 - Change old bailout fix to only apply to Clang versions older than 5.0 and add new fix with -gdwarf-aranges + -gdwarf-4 for Clang 5.0+
 - 8293422: DWARF emitted by Clang cannot be parsed

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Changes: https://git.openjdk.org/jdk/pull/10287/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=10287&range=06
  Stats: 162 lines in 5 files changed: 113 ins; 31 del; 18 mod
  Patch: https://git.openjdk.org/jdk/pull/10287.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/10287/head:pull/10287

PR: https://git.openjdk.org/jdk/pull/10287