RFR: 8353009: Document target selection flag for Windows AArch64 builds [v2]

[Saint Wesonga]

> The target selection configuration flag for Windows AArch64 should be added to the build documentation for improved discoverability and completeness.

Saint Wesonga has updated the pull request incrementally with one additional commit since the last revision:

  Clarify that instructions are for cross compilation

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Changes:
  - all: https://git.openjdk.org/jdk/pull/24267/files
  - new: https://git.openjdk.org/jdk/pull/24267/files/c15306a8..8cb94d9b

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=24267&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=24267&range=00-01

  Stats: 7 lines in 2 files changed: 2 ins; 0 del; 5 mod
  Patch: https://git.openjdk.org/jdk/pull/24267.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/24267/head:pull/24267

PR: https://git.openjdk.org/jdk/pull/24267