Simplify a bit pre-compiler conditions.

For TSAN, QEMU already has CONFIG_TSAN, but it is only set when the
fiber API is present. (I wonder whether supporting TSAN without the
fiber API is really relevant)

Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
Message-Id: <20220420132624.2439741-27-marcandre.lureau@redhat.com>