[jdk16u] RFR: 8259049: Uninitialized variable after JDK-8257513

[Tobias Hartmann]

Backport of [JDK-8257513](https://bugs.openjdk.java.net/browse/JDK-8257513). Applies cleanly.

-------------

Commit messages:
 - 8257513: C2: assert((constant_addr - _masm.code()->consts()->start()) == con.offset())

Changes: https://git.openjdk.java.net/jdk16u/pull/17/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk16u&pr=17&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8259049
  Stats: 91 lines in 4 files changed: 82 ins; 0 del; 9 mod
  Patch: https://git.openjdk.java.net/jdk16u/pull/17.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk16u pull/17/head:pull/17

PR: https://git.openjdk.java.net/jdk16u/pull/17