Update librseq to co-exist with glibc rseq integration

Update librseq to co-exist with glibc rseq integration

Update librseq to co-exist with the rseq integration merged within the
glibc 2.35 release cycle.

librseq exposes its own "rseq_offset, rseq_size, rseq_flags" ABI.

Query for glibc rseq ABI (__rseq_offset, __rseq_size, __rseq_flags)
using dlsym() in a librseq library constructor. If those are found,
copy their values into rseq_offset, rseq_size, and rseq_flags.

Else, if those glibc symbols are not found, handle rseq registration
ourselves and use our own IE-model TLS to implement the rseq ABI
per-thread storage.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Change-Id: I1220cb5c31e823e9cddf211ec56fee03b729b137