runtime: ignore GNU/Linux sigaction errors for signals 32 and 33
runtime: ignore GNU/Linux sigaction errors for signals 32 and 33

This avoids problems when running under QEMU. It seems that at least
some QEMU versions turn the sigaction implementation into a call to
the C library sigaction function. The C library function will reject
attempts to set the signal handler for signals 32 and 33. Ignore
errors in that case.

Change-Id: Id443a9a32f6fb0ceef5c59a398e7ede30bf71646
Reviewed-on: https://go-review.googlesource.com/125955
Run-TryBot: Ian Lance Taylor <87e9c6d529889242b7e184afb632328636553ab4@golang.org>
Reviewed-by: Heschi Kreinick <e89ab2b172855aa0ad01c40c4d8a3535a61ac68a@google.com>
TryBot-Result: Gobot Gobot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>

cloudflare/go,cloudflare/go,CAFxX/go,cloudflare/go,CAFxX/go,josharian/go,golang/go,golang/go,nawawi/go,golang/go,josharian/go,nawawi/go,akutz/go,akutz/go,akutz/go,akutz/go,golang/go,CAFxX/go,nawawi/go,nawawi/go,josharian/go,CAFxX/go,golang/go,CAFxX/go,akutz/go,golang/go,nawawi/go,golang/go,nawawi/go,golang/go,cloudflare/go,CAFxX/go,nawawi/go,josharian/go,nawawi/go,cloudflare/go,akutz/go,josharian/go,cloudflare/go,CAFxX/go,josharian/go,akutz/go,cloudflare/go,cloudflare/go,josharian/go,CAFxX/go,josharian/go,akutz/go