RFR: 8343607: C2: Shenandoah crashes during barrier expansion in Continuation::enter

[Roland Westrelin]

If a load barrier is used both in the fallthrough and exception
handling paths out of a call, it needs to be cloned so each path has
its copy of the barrier. In the case of the crash, cloning the barrier
is attempted for a runtime call that doesn't have an exception
handling path. Fix simply detects that corner case.

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Commit messages:
 - fix

Changes: https://git.openjdk.org/jdk/pull/22663/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=22663&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8343607
  Stats: 10 lines in 1 file changed: 9 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/22663.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/22663/head:pull/22663

PR: https://git.openjdk.org/jdk/pull/22663