RFR(S) 8244775 Remove unnecessary dependency to jfrEvents.hpp

[Ioi Lam]

https://bugs.openjdk.java.net/browse/JDK-8244775
http://cr.openjdk.java.net/~iklam/jdk15/8244775-remove-dependency-jfrEvents.hpp.v01/

Currently 231 .o files depends on jfrEvents.hpp, which pulls in a lot of 
stuff
and slows down HotSpot build.

I refactored compile.hpp, compilerEvent.hpp and g1GCPhaseTimes.hpp. Now the
number is down to 65 .o files.

On my machine, debug build goes from 2m19s to 2m01s.

Testing: passed mach5 tiers 1/2/3.

Thanks
- Ioi