With the global redefinition of runtime·open by CL 7543043,
we need to provide a third argument and remove the cast
to the string.
Fixes build on 386 version of Plan 9.
R=khr, rsc, rminnich, ality
CC=golang-dev
https://golang.org/cl/7644047
Separates the implementation of nanotime on 64-bit
version of Plan 9 from that on the 32-bit version.
The former uses a syscall.
R=rsc, rminnich, ality
CC=golang-dev
https://golang.org/cl/7379051