RFR (XXS): 8064348: Add TraceEvent::is_enabled() for embedded/minimal builds

[Marcus Larsson]

Hi,

Can I please have reviews for the following small patch to enable usage 
of TraceEvent::is_enabled() even when INCLUDE_TRACE is not defined?

Webrev:
http://cr.openjdk.java.net/~mlarsson/8064348/webrev.00/

Bug:
https://bugs.openjdk.java.net/browse/JDK-8064348

Thanks,
Marcus