RFR: 8292919: Build failure due to UseJVMCICompiler was not declared when C2 is disabled after JDK-8292691

[Jie Fu]

Hi all,

Please review this trivial fix which fixes the build failure when C2 is disabled due to the definition of `UseJVMCICompiler` is missing.

Thanks.
Best regards,
Jie

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Commit messages:
 - 8292919: Build failure due to UseJVMCICompiler was not declared when C2 is disabled after JDK-8292691

Changes: https://git.openjdk.org/jdk/pull/10027/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=10027&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8292919
  Stats: 3 lines in 1 file changed: 3 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/10027.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/10027/head:pull/10027

PR: https://git.openjdk.org/jdk/pull/10027