gcc: backport xtensa libgcc stack unwinding fixes
These backported patches fix the following failing uClibc-ng tests:
nptl/tst-cancelx4,
nptl/tst-cancelx16,
nptl/tst-cancelx18,
nptl/tst-cancelx20,
nptl/tst-cancelx21,
nptl/tst-cleanupx1,
nptl/tst-cleanupx3,
nptl/tst-oncex3,
nptl/tst-oncex4.
Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>