RFR(XS): 8242796: Fix client build failure

[Yang Zhang]

Hi,

Could you please help to review this patch?

JBS: https://bugs.openjdk.java.net/browse/JDK-8242796
Webrev: http://cr.openjdk.java.net/~yzhang/8242796/webrev.00/

This build failure is introduced by JDK-8193210 [JVMCI/Graal] add JFR
compiler phase/inlining events.
C2 only code is used for JFR. To fix this issue, I use COMPILER2 macro.

With this patch, x86 client build succeeds. But AArch64 client build
still fails, which is caused by [1]. I have filed [2] for AArch64
client build failure and will summit another patch for that.

[1] https://bugs.openjdk.java.net/browse/JDK-8241665
[2] https://bugs.openjdk.java.net/browse/JDK-8242905

Regards
Yang