[jdk13u-dev] RFR: 8274293: Build failure on macOS with Xcode 13.0 as vfork is deprecated

[Olga Mikhaltsova]

I'd like to backport JDK-8274293 to jdk13u for parity with jdk11u. 
The same issue is observed on macOS Monterey 12.0.1 while compiling with Xcode 13.0 (--disable-warnings-as-errors is used because it's not the only issue at the moment):

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Commit messages:
 - Backport 252aaa9249d8979366b37d59487b5b039d923e35

Changes: https://git.openjdk.java.net/jdk13u-dev/pull/292/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk13u-dev&pr=292&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8274293
  Stats: 4 lines in 1 file changed: 0 ins; 0 del; 4 mod
  Patch: https://git.openjdk.java.net/jdk13u-dev/pull/292.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk13u-dev pull/292/head:pull/292

PR: https://git.openjdk.java.net/jdk13u-dev/pull/292