[jdk17u-dev] RFR: 8298527: Cygwin's uname -m returns different string than before

[Christoph Langer]

Backport of a small build system fix/cleanup. I had to resolve because RISCV was not handled in jdk17u-dev yet.
For this backport, in the new code, I chose to leave the RISCV branch in. It should do no harm.

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Commit messages:
 - Backport 51f0a1ce4b0d72cf7e82e01f7014274d8b7d1575

Changes: https://git.openjdk.org/jdk17u-dev/pull/959/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk17u-dev&pr=959&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8298527
  Stats: 64 lines in 1 file changed: 33 ins; 30 del; 1 mod
  Patch: https://git.openjdk.org/jdk17u-dev/pull/959.diff
  Fetch: git fetch https://git.openjdk.org/jdk17u-dev pull/959/head:pull/959

PR: https://git.openjdk.org/jdk17u-dev/pull/959