RFR: 8307969: [zgc] Missing includes in gc/z/zTracer.cpp [v2]

[Jie Fu]

> This fixes the build broken with `--with-jvm-features=-jfr`.
> Thanks.

Jie Fu has updated the pull request incrementally with one additional commit since the last revision:

  Address review comment

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/13948/files
  - new: https://git.openjdk.org/jdk/pull/13948/files/149633f3..1a5411f8

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=13948&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=13948&range=00-01

  Stats: 1 line in 1 file changed: 0 ins; 1 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/13948.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/13948/head:pull/13948

PR: https://git.openjdk.org/jdk/pull/13948