RFR: 8276672: Cannot build hsdis on WSL

[Yasumasa Suenaga]

JDK-8275128 introduced new Makefile for hsdis to integrate it to normal build system, however it does not work on WSL 1 Ubuntu 20.04 and MinGW from Ubuntu.

Hsdis.gmk has two problems:

1. MinGW version is fixed to "9.2.0"
2. Assumes sysroot for MinGW is located at /usr/$MINGW_BASE/sys-root

I tested this change on WSL only, so it is appreciate to review on Cygwin.

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Commit messages:
 - 8276672: Cannot build hsdis on WSL

Changes: https://git.openjdk.java.net/jdk/pull/6269/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=6269&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8276672
  Stats: 13 lines in 1 file changed: 8 ins; 0 del; 5 mod
  Patch: https://git.openjdk.java.net/jdk/pull/6269.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/6269/head:pull/6269

PR: https://git.openjdk.java.net/jdk/pull/6269