runtime: loop on EINTR in macOS sigNoteSleep

Fixes #46466

Change-Id: I8fb15d0c8ef7ef6e6fc1b9e0e033d213255fe0df
Reviewed-on: https://go-review.googlesource.com/c/go/+/326778
Trust: Ian Lance Taylor <iant@golang.org>
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Michael Knyszek <mknyszek@google.com>
Reviewed-by: Cherry Mui <cherryyz@google.com>

src/runtime/os_darwin.go

@@ -118,10 +118,15 @@ func sigNoteWakeup(*note) {
 
 // sigNoteSleep waits for a note created by sigNoteSetup to be woken.
 func sigNoteSleep(*note) {
-	entersyscallblock()
-	var b byte
-	read(sigNoteRead, unsafe.Pointer(&b), 1)
-	exitsyscall()
+	for {
+		var b byte
+		entersyscallblock()
+		n := read(sigNoteRead, unsafe.Pointer(&b), 1)
+		exitsyscall()
+		if n != -_EINTR {
+			return
+		}
+	}
 }
 
 // BSD interface for threading.