syscall: fix build directive in types_linux.go
syscall: fix build directive in types_linux.go

The rule is that build directives can be preceded only
by blank lines and other line comments, not /* */ comments.

R=golang-dev, adg, bradfitz
CC=golang-dev
http://codereview.appspot.com/5619045
abustany/go,abustany/go,abustany/go,abustany/go,abustany/go,abustany/go,abustany/go