Windows: Factor out seccomp

Signed-off-by: John Howard <jhoward@microsoft.com>

libcontainer/seccomp/bpf.go

@@ -1,3 +1,5 @@
+// +build linux
+
 package seccomp
 
 import "strings"

libcontainer/seccomp/context.go

@@ -1,3 +1,5 @@
+// +build linux
+
 package seccomp
 
 import (

libcontainer/seccomp/filter.go

@@ -1,3 +1,5 @@
+// +build linux
+
 package seccomp
 
 import (

libcontainer/seccomp/seccomp_unix.go

@@ -1,3 +1,5 @@
+// +build linux
+
 // Package seccomp provides native seccomp ( https://www.kernel.org/doc/Documentation/prctl/seccomp_filter.txt ) support for go.
 package seccomp
 

libcontainer/seccomp/seccomp_unsupported.go

@@ -0,0 +1,3 @@
+// +build !linux
+
+package seccomp