tools/virtio: compile with -pthread

stable inclusion
from stable-v5.10.118
commit 3663d6023aa2198f7d3eb55cc7797b1f9fff7659
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I5L686

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=3663d6023aa2198f7d3eb55cc7797b1f9fff7659



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[ Upstream commit f03560a5 ]

When using pthreads, one has to compile and link with -lpthread,
otherwise e.g. glibc is not guaranteed to be reentrant.

This replaces -lpthread.

Reported-by: Matthew Wilcox <willy@infradead.org>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Zheng Zengkai <zhengzengkai@huawei.com>
Acked-by: Xie XiuQi <xiexiuqi@huawei.com>