runtime: profiling on Darwin cannot use blocking reads
On Darwin (and assume also on iOS but not sure), notetsleepg
cannot be called in a signal-handling context. Avoid this
by disabling block reads on Darwin.
An alternate approach was to add "sigNote" with a pipe-based
implementation on Darwin, but that ultimately would have required
at least one more linkname between runtime and syscall to avoid
racing with fork and opening the pipe, so, not.
Fixes #61768.
Change-Id: I0e8dd4abf9a606a3ff73fc37c3bd75f55924e07e
Reviewed-on: https://go-review.googlesource.com/c/go/+/518836
Run-TryBot: David Chase <drchase@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org> Reviewed-by: Michael Knyszek <mknyszek@google.com>