Merge pull request #49300 from tklauser/syscall-to-x-sys-unix

Automatic merge from submit-queue

Switch from package syscall to golang.org/x/sys/unix

**What this PR does / why we need it**:

The syscall package is locked down and the comment in https://github.com/golang/go/blob/master/src/syscall/syscall.go#L21-L24 advises to switch code to use the corresponding package from golang.org/x/sys. This PR does so and replaces usage of package syscall with package golang.org/x/sys/unix where applicable. This will also allow to get updates and fixes
without having to use a new go version.

In order to get the latest functionality, golang.org/x/sys/ is re-vendored. This also allows to use Eventfd() from this package instead of calling the eventfd() C function.

**Special notes for your reviewer**:

This follows previous works in other Go projects, see e.g. moby/moby#33399, cilium/cilium#588

**Release note**:

```release-note
NONE
```

staging/src/k8s.io/apiextensions-apiserver/Godeps/Godeps.json

@@ -344,7 +344,7 @@
 		},
 		{
 			"ImportPath": "golang.org/x/sys/unix",
-			"Rev": "8f0908ab3b2457e2e15403d3697c9ef5cb4b57a9"
+			"Rev": "7a4fde3fda8ef580a89dbae8138c26041be14299"
 		},
 		{
 			"ImportPath": "golang.org/x/text/cases",

staging/src/k8s.io/apiserver/Godeps/Godeps.json

@@ -620,7 +620,7 @@
 		},
 		{
 			"ImportPath": "golang.org/x/sys/unix",
-			"Rev": "8f0908ab3b2457e2e15403d3697c9ef5cb4b57a9"
+			"Rev": "7a4fde3fda8ef580a89dbae8138c26041be14299"
 		},
 		{
 			"ImportPath": "golang.org/x/text/cases",

staging/src/k8s.io/client-go/Godeps/Godeps.json

@@ -272,7 +272,7 @@
 		},
 		{
 			"ImportPath": "golang.org/x/sys/unix",
-			"Rev": "8f0908ab3b2457e2e15403d3697c9ef5cb4b57a9"
+			"Rev": "7a4fde3fda8ef580a89dbae8138c26041be14299"
 		},
 		{
 			"ImportPath": "golang.org/x/text/cases",

staging/src/k8s.io/kube-aggregator/Godeps/Godeps.json

@@ -340,7 +340,7 @@
 		},
 		{
 			"ImportPath": "golang.org/x/sys/unix",
-			"Rev": "8f0908ab3b2457e2e15403d3697c9ef5cb4b57a9"
+			"Rev": "7a4fde3fda8ef580a89dbae8138c26041be14299"
 		},
 		{
 			"ImportPath": "golang.org/x/text/cases",

staging/src/k8s.io/sample-apiserver/Godeps/Godeps.json

@@ -332,7 +332,7 @@
 		},
 		{
 			"ImportPath": "golang.org/x/sys/unix",
-			"Rev": "8f0908ab3b2457e2e15403d3697c9ef5cb4b57a9"
+			"Rev": "7a4fde3fda8ef580a89dbae8138c26041be14299"
 		},
 		{
 			"ImportPath": "golang.org/x/text/cases",