git: openjdk/loom: fibers: convert c-based vthread tests to c++ tests

[duke]

Changeset: 2dc47a13
Author:    Serguei Spitsyn <serguei.spitsyn at oracle.com>
Date:      2021-02-18 05:46:41 +0000
URL:       https://git.openjdk.java.net/loom/commit/2dc47a13

convert c-based vthread tests to c++ tests

- test/hotspot/jtreg/serviceability/jvmti/vthread/VThreadMonitorTest/libVThreadMonitorTest.c
+ test/hotspot/jtreg/serviceability/jvmti/vthread/VThreadMonitorTest/libVThreadMonitorTest.cpp
- test/hotspot/jtreg/serviceability/jvmti/vthread/VThreadTest/libVThreadTest.c
+ test/hotspot/jtreg/serviceability/jvmti/vthread/VThreadTest/libVThreadTest.cpp
- test/hotspot/jtreg/serviceability/jvmti/vthread/VThreadUnsupportedTest/libVThreadUnsupportedTest.c
+ test/hotspot/jtreg/serviceability/jvmti/vthread/VThreadUnsupportedTest/libVThreadUnsupportedTest.cpp