[jdk13u-dev] RFR: 8257633: Missing -mmacosx-version-min=X flag when linking libjvm

[Vladimir Kempik]

Please review this small changeset. Build-system only change.
Backport didn't apply cleanly due to context code differences, the patched code is the same.
After the fix applied, libjvm has both sha1 and sha256 signatures, which will allow it to run on older macos.

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Commit messages:
 - 8257633: Missing -mmacosx-version-min=X flag when linking libjvm

Changes: https://git.openjdk.java.net/jdk13u-dev/pull/79/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk13u-dev&pr=79&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8257633
  Stats: 3 lines in 1 file changed: 0 ins; 0 del; 3 mod
  Patch: https://git.openjdk.java.net/jdk13u-dev/pull/79.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk13u-dev pull/79/head:pull/79

PR: https://git.openjdk.java.net/jdk13u-dev/pull/79