runtime: use urandom instead of random

Random is bad, it can block and prevent binaries from starting.
Use urandom instead.  We'd rather have bad random bits than no
random bits.

Change-Id: I360e1cb90ace5518a1b51708822a1dae27071ebd
Reviewed-on: https://go-review.googlesource.com/2582
Reviewed-by: Dave Cheney <dave@cheney.net>
Reviewed-by: Minux Ma <minux@golang.org>

src/runtime/os1_darwin.go

@@ -45,7 +45,7 @@ func osinit() {
 	}
 }
 
-var urandom_dev = []byte("/dev/random\x00")
+var urandom_dev = []byte("/dev/urandom\x00")
 
 //go:nosplit
 func getRandomData(r []byte) {