RFR: 8340980: Cannot build on Windows ARM

[Martin Fox]

Restored some behavior in genVSproperties that enabled ARM builds and cross-compilation on Windows. Verified that I can build on ARM but have no way of testing other architectures.

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Commit messages:
 - Restored some lost behavior that enabled ARM builds on Windows

Changes: https://git.openjdk.org/jfx/pull/1580/files
  Webrev: https://webrevs.openjdk.org/?repo=jfx&pr=1580&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8340980
  Stats: 2 lines in 1 file changed: 0 ins; 0 del; 2 mod
  Patch: https://git.openjdk.org/jfx/pull/1580.diff
  Fetch: git fetch https://git.openjdk.org/jfx.git pull/1580/head:pull/1580

PR: https://git.openjdk.org/jfx/pull/1580