RFR (S) 8218151: Simplify JavaThread::thread_state definition

[Aleksey Shipilev]

RFE:
  https://bugs.openjdk.java.net/browse/JDK-8218151

Fix:
  http://cr.openjdk.java.net/~shade/8218151/webrev.01/

The difference in definitions in JavaThread::thread_state in AArch64 and PPC64 is the source of
frequent build failures when someone tests only x86_64, see the linked issues for a taste. The way
out of this is to push the #if-s inside the method body, so that definition is always in one place,
and would not accidentally break the build.

Testing: Linux {x86_64, x86_32, aarch64, arm32, ppc64el, s390x} builds, Mac OS X {x86_64} build,
Windows {x86_64} build, jdk-submit (failed windows test and macos build, but I suspect there are
infra problems, will wait and re-run; see for example mach5-one-shade-JDK-8218151-20190131-1631-233989).

Thanks,
-Aleksey