selftests/rseq: check if libc rseq support is registered

mainline inclusion
from mainline-v6.0-rc1
commit d1a997ba
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I69PT8

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=d1a997ba4c1bf65497d956aea90de42a6398f73a



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commit d1a997ba upstream.

When checking for libc rseq support in the library constructor, don't
only depend on the symbols presence, check that the registration was
completed.

This targets a scenario where the libc has rseq support but it is not
wired for the current architecture in 'bits/rseq.h', we want to fallback
to our internal registration mechanism.

Signed-off-by: Michael Jeanson <mjeanson@efficios.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Link: https://lore.kernel.org/r/20220614154830.1367382-4-mjeanson@efficios.com


Signed-off-by: rminmin <renmm6@chinaunicom.cn>