[jdk13u-dev] RFR: 8256501: libTestMainKeyWindow fails to build with Xcode 12.2

[Vladimir Kempik]

Clean backport to jdk13u-dev. A prerequest for the jnf_removal patches to apply more cleanly.

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Commit messages:
 - Backport 4e5116c46e29977cccbe8c04cb5559ce345fa72e

Changes: https://git.openjdk.java.net/jdk13u-dev/pull/168/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk13u-dev&pr=168&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8256501
  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.java.net/jdk13u-dev/pull/168.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk13u-dev pull/168/head:pull/168

PR: https://git.openjdk.java.net/jdk13u-dev/pull/168