runtime: allow for usleep2HighRes to run without TLS setup
This change adjusts usleep2HighRes so it does not crash when TLS is
not configured. When g is not available, usleep2HighRes just calls
usleep2 instead.
Updates #8687
Change-Id: Idbb80f7b71d1da350a6a7df7c49154eb1ffe29a8
Reviewed-on: https://go-review.googlesource.com/c/go/+/271907
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TryBot-Result: Go Bot <gobot@golang.org> Reviewed-by: Jason A. Donenfeld <Jason@zx2c4.com> Reviewed-by: Simon Rozman <simon@rozman.si>
Trust: Jason A. Donenfeld <Jason@zx2c4.com>
Trust: Alex Brainman <alex.brainman@gmail.com>