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

[Ludovic Henry]

> When bringing up Hotspot onto new platforms, it is not always possible to compile hsdis because gcc is not yet
> available. For example, for Windows-AArch64 and macOS-AArch64.
> For some such platforms, it is possible to use LLVM as an alternative backend as it also supports a disassembler
> feature.

Ludovic Henry has updated the pull request incrementally with two additional commits since the last revision:

 - Fix compiler warnings
 - Reduce amount of error messages when failing to initialize LLVM

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

Changes:
  - all: https://git.openjdk.java.net/jdk/pull/392/files
  - new: https://git.openjdk.java.net/jdk/pull/392/files/a551e247..c497b30f

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=392&range=03
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=392&range=02-03

  Stats: 29 lines in 1 file changed: 19 ins; 2 del; 8 mod
  Patch: https://git.openjdk.java.net/jdk/pull/392.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/392/head:pull/392

PR: https://git.openjdk.java.net/jdk/pull/392