Fix unwind on ARM64 Linux (#20345)

Fix unwind on ARM64 Linux (#20345)

The libunwind cannot unwind from `__libc_start_main` to `_start` on
Linux ARM64 with glibc <= 2.27, because the `__libc_start_main` is
missing unwind info. While we already have a way to detect such case
when the same issue happens for `_start`, we were triggering it only in
case unw_step returned 0. For this case, it returns 1 though, which is
also a valid success indicator.
The result is that .NET core starts spinning infinitely in case an
unhandled exception happens on ARM64.
The fix is to update the check to test for the return value being >= 0.