RFR: 8253757: Add LLVM-based backend for hsdis

[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.

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Commit messages:
 - Create hsdis backend using LLVM

Changes: https://git.openjdk.java.net/jdk/pull/5920/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=5920&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8253757
  Stats: 406 lines in 6 files changed: 398 ins; 0 del; 8 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