[jdk11u-dev] RFR: 8210960: Allow --with-boot-jdk-jvmargs to work during configure

[George Adams]

clean backport - makes https://bugs.openjdk.org/browse/JDK-8239708 apply more cleanly.

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Commit messages:
 - Backport a32f8e382d31fdb90f2e7ca5d82710dae39e1cc8

Changes: https://git.openjdk.org/jdk11u-dev/pull/1271/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk11u-dev&pr=1271&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8210960
  Stats: 25 lines in 2 files changed: 16 ins; 4 del; 5 mod
  Patch: https://git.openjdk.org/jdk11u-dev/pull/1271.diff
  Fetch: git fetch https://git.openjdk.org/jdk11u-dev pull/1271/head:pull/1271

PR: https://git.openjdk.org/jdk11u-dev/pull/1271