RFR: 8284369: TestFailedAllocationBadGraph fails with -XX:TieredStopAtLevel < 4

[Tobias Hartmann]

Trivial fix that adds a missing `@requires` to guard against the case when C2 is not available (for example, when `TieredStopAtLevel < 4`).

Thanks,
Tobias

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Commit messages:
 - 8284369: TestFailedAllocationBadGraph fails with -XX:TieredStopAtLevel < 4

Changes: https://git.openjdk.java.net/jdk/pull/8118/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=8118&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8284369
  Stats: 2 lines in 1 file changed: 1 ins; 0 del; 1 mod
  Patch: https://git.openjdk.java.net/jdk/pull/8118.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/8118/head:pull/8118

PR: https://git.openjdk.java.net/jdk/pull/8118