git: openjdk/loom: fibers: fix build issue on Windows in VthreadTest

[duke]

Changeset: 260a3d0e
Author:    Serguei Spitsyn <serguei.spitsyn at oracle.com>
Date:      2021-02-18 09:02:52 +0000
URL:       https://git.openjdk.java.net/loom/commit/260a3d0e

fix build issue on Windows in VthreadTest

! test/hotspot/jtreg/serviceability/jvmti/vthread/VThreadTest/libVThreadTest.cpp
! test/hotspot/jtreg/serviceability/jvmti/vthread/VThreadUnsupportedTest/libVThreadUnsupportedTest.cpp