[jdk21u] RFR: 8308585: AC_REQUIRE: `PLATFORM_EXTRACT_TARGET_AND_BUILD' was expanded before it was required

[Erik Joelsson]

Should be a clean backport of this build warning fix.

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Commit messages:
 - Backport 554b4d7243f2c7bb3cc3260358fc7c3c636d7536

Changes: https://git.openjdk.org/jdk21u/pull/5/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk21u&pr=5&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8308585
  Stats: 5 lines in 2 files changed: 1 ins; 1 del; 3 mod
  Patch: https://git.openjdk.org/jdk21u/pull/5.diff
  Fetch: git fetch https://git.openjdk.org/jdk21u.git pull/5/head:pull/5

PR: https://git.openjdk.org/jdk21u/pull/5