RFR: 8286647: JFR: Build failure when C1 or C2 is disabled after JDK-8282420

[Jie Fu]

Hi all,

JDK fails to build when c1 or c2 is disabled after JDK-8282420.
The reason is that c1/c2 code is used without `#ifdef` guards.
The fix just adds some `#ifdef`.

Testing:
 - build   on Linux/x64
 - jdk/jfr on Linux/x64

Thanks.
Best regards,
Jie

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Commit messages:
 - 8286647: JFR: Build failure when C1 or C2 is disabled after JDK-8282420

Changes: https://git.openjdk.java.net/jdk/pull/8680/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=8680&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8286647
  Stats: 32 lines in 3 files changed: 28 ins; 4 del; 0 mod
  Patch: https://git.openjdk.java.net/jdk/pull/8680.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/8680/head:pull/8680

PR: https://git.openjdk.java.net/jdk/pull/8680