Bug 575483 - Eclipse may forget to build

hasBuildChanges should be volatile, setBuild() synchronized

Change-Id: I420925f064dd3f4c7ba08d1710a605f5da46c086
Signed-off-by: Andrey Loskutov <loskutov@gmx.de>
Reviewed-on: https://git.eclipse.org/r/c/platform/eclipse.platform.resources/+/184202
Reviewed-by: Jörg Kubitz <jkubitz-eclipse@gmx.de>