RFR(trivial): 8233574: Shenandoah: build is broken without jfr

[Jie Fu]

Hi all,

May I get reviews for the one-line change?
This bug was found while I was testing David's patch for JDK-8233454 [1].

JBS:    https://bugs.openjdk.java.net/browse/JDK-8233574
Webrev: http://cr.openjdk.java.net/~jiefu/8233574/webrev.00/

Thanks a lot.
Best regards,
Jie

[1] 
https://mail.openjdk.java.net/pipermail/hotspot-runtime-dev/2019-November/036788.html