RFR: 8253757: Add LLVM-based backend for hsdis [v4]

[Magnus Ihse Bursie]

> This patch expands the newly added system for hsdis backends to include LLVM.
> 
> The actual code in hsdis-llvm.cpp is based heavily on the work by @luhenry, as published in the never integrated PR https://github.com/openjdk/jdk/pull/392. (I have basically just ripped out the binutils-based part of it.)
> 
> Unfortunately I have not been able to make this work properly on Windows. With some additional flags I made it compile without complaints, but it caused hotspot to segfault in `LoadLibrary` (!) in `os::dll_load` when I tried to load the library. This is somewhat ironic, since the initial implementation was created by Ludovic for the very purpose of using it on Windows.
> 
> The lack of Windows support in this patch does not mean it is impossible to get it to work, just that I need to co-operate with someone who has more experience of compiling LLVM on Windows, and/or are more eager to get this combination to work.

Magnus Ihse Bursie has updated the pull request incrementally with one additional commit since the last revision:

  Handle unknown instructions from LLVM. Solution suggested by ngasson.

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Changes:
  - all: https://git.openjdk.java.net/jdk/pull/5920/files
  - new: https://git.openjdk.java.net/jdk/pull/5920/files/9f2ab6d9..7d866725

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=5920&range=03
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=5920&range=02-03

  Stats: 9 lines in 1 file changed: 9 ins; 0 del; 0 mod
  Patch: https://git.openjdk.java.net/jdk/pull/5920.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/5920/head:pull/5920

PR: https://git.openjdk.java.net/jdk/pull/5920