After fixing libunwind issues in 7dc9fe44, libcoro fibers issues in
761053f0 and c8ad49f0, we can now re-enable backtrace feature on
AARCH64.

For some not investigated reason `unw_backtrace` does not collect any
ips when "-mbranch-protection" compile feature is enabled: provide a
workaround for this case.

Closes #6060

NO_DOC=build system
NO_TEST=build system