RFR: 8253757: Add LLVM-based backend for hsdis

[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.

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Commit messages:
 - 8253757: Add LLVM-based backend for hsdis

Changes: https://git.openjdk.java.net/jdk/pull/392/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=392&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8253757
  Stats: 534 lines in 3 files changed: 534 ins; 0 del; 0 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