KVM: selftests: Make rseq compatible with glibc-2.35

The rseq information is registered by TLS, starting from glibc-2.35.
In this case, the test always fails due to syscall(__NR_rseq). For
example, on RHEL9.1 where upstream glibc-2.35 features are enabled
on downstream glibc-2.34, the test fails like below.

  # ./rseq_test
  ==== Test Assertion Failure ====
    rseq_test.c:60: !r
    pid=112043 tid=112043 errno=22 - Invalid argument
       1        0x0000000000401973: main at rseq_test.c:226
       2        0x0000ffff84b6c79b: ?? ??:0
       3        0x0000ffff84b6c86b: ?? ??:0
       4        0x0000000000401b6f: _start at ??:?
    rseq failed, errno = 22 (Invalid argument)
  # rpm -aq | grep glibc-2
  glibc-2.34-39.el9.aarch64

Fix the issue by using "../rseq/rseq.c" to fetch the rseq information,
registred by TLS if it exists. Otherwise, we're going to register our
own rseq information as before.

Reported-by: Yihuang Yu <yihyu@redhat.com>
Suggested-by: Florian Weimer <fweimer@redhat.com>
Suggested-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Suggested-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Gavin Shan <gshan@redhat.com>
Message-Id: <20220810104114.6838-2-gshan@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>