runtime: faster chan creation on Linux/FreeBSD/Plan9
The change removes chan finalizer (Lock destructor)
if it is not required on the platform.
benchmark old ns/op new ns/op delta
BenchmarkChanCreation 1132.00 381.00 -66.34%
BenchmarkChanCreation-2 1215.00 243.00 -80.00%
BenchmarkChanCreation-4 1084.00 186.00 -82.84%
BenchmarkChanCreation-8 1415.00 154.00 -89.12%
BenchmarkChanCreation-16 1386.00 144.00 -89.61%
(on 2 x Intel Xeon E5620, 8 HT cores, 2.4 GHz, Linux)
R=golang-dev, rsc
CC=golang-dev
https://golang.org/cl/
4841041