git: openjdk/loom: fibers: jthread not defined in jni.h, revert

[duke]

Changeset: d52569ef
Author:    mgronlun <markus.gronlund at oracle.com>
Date:      2020-02-06 10:09:44 +0000
URL:       https://git.openjdk.java.net/loom/commit/d52569ef

jthread not defined in jni.h, revert

! src/hotspot/share/jfr/jfr.cpp
! src/hotspot/share/jfr/jfr.hpp
! src/hotspot/share/jfr/jni/jfrJavaSupport.cpp
! src/hotspot/share/jfr/jni/jfrJavaSupport.hpp
! src/hotspot/share/jfr/support/jfrThreadLocal.cpp
! src/hotspot/share/jfr/support/jfrThreadLocal.hpp