git: openjdk/loom: fibers: fix build on Windows: type conversion issue

[duke]

Changeset: bf976113
Author:    Serguei Spitsyn <serguei.spitsyn at oracle.com>
Date:      2021-04-01 03:31:46 +0000
URL:       https://git.openjdk.java.net/loom/commit/bf976113

fix build on Windows: type conversion issue

! test/lib/jdk/test/lib/jvmti/jvmti_common.h