syscall: mark C syscall functions noescape

Many C syscall functions take pointer arguments. The pointers
don't escape in the C functions. Mark the C functions noescape so
calling them doesn't need allocation.

Change-Id: Ifa5a5d0de51c4af9d1bb16b3fbfc166632ee2711
Reviewed-on: https://go-review.googlesource.com/c/158158
Reviewed-by: Ian Lance Taylor <iant@golang.org>
2 files changed