unix: merge duplicate code in zsyscall_linux_*.go

Run mkmerge.go on zsyscall_linux_*.go to merge duplicate consts, funcs,
and types into zsyscall_linux.go

Also, run mkmerge.go on zsysnum_linux_*.go; currently there is nothing
to merge.

Please see https://gist.github.com/jupj/639b5cda305d251161fec2304c27c9b9
for a script to validate these changes.

Updates golang/go#33059

Change-Id: I715ada044ee957475669d94b16de059ebb9162d1
Reviewed-on: https://go-review.googlesource.com/c/sys/+/221319
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

unix/linux/mkall.go

@@ -563,7 +563,7 @@ func mergeFiles() error {
 	os.Setenv("GOARCH", runtime.GOARCH)
 
 	// Merge each of the four type of files
-	for _, ztyp := range []string{"zerrors"} {
+	for _, ztyp := range []string{"zerrors", "zsyscall", "zsysnum"} {
 		cmd := makeCommand("go", "run", "mkmerge.go", "-out", fmt.Sprintf("%s_%s.go", ztyp, GOOS), fmt.Sprintf("%s_%s_*.go", ztyp, GOOS))
 		err := cmd.Run()
 		if err != nil {