all: simplify code by using modern Go constructs

Generated using modernize by running:

    go run golang.org/x/tools/gopls/internal/analysis/modernize/cmd/modernize@latest -fix -test ./...

Change-Id: Ifc7d61cf6735cc53f2bdf890a338961f55075af5
Reviewed-on: https://go-review.googlesource.com/c/sys/+/661975
Auto-Submit: Tobias Klauser <tobias.klauser@gmail.com>
Reviewed-by: Carlos Amedee <carlos@golang.org>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>

unix/internal/mkmerge/mkmerge.go

@@ -137,7 +137,7 @@ type filterFn func(codeElem) bool
 // filter parses and filters Go source code from src, removing top
 // level declarations using keep as predicate.
 // For src parameter, please see docs for parser.ParseFile.
-func filter(src interface{}, keep filterFn) ([]byte, error) {
+func filter(src any, keep filterFn) ([]byte, error) {
 	// Parse the src into an ast
 	fset := token.NewFileSet()
 	f, err := parser.ParseFile(fset, "", src, parser.ParseComments)
@@ -243,7 +243,7 @@ func getCommonSet(files []srcFile) (*codeSet, error) {
 
 // getCodeSet returns the set of all top-level consts, types, and funcs from src.
 // src must be string, []byte, or io.Reader (see go/parser.ParseFile docs)
-func getCodeSet(src interface{}) (*codeSet, error) {
+func getCodeSet(src any) (*codeSet, error) {
 	set := newCodeSet()
 
 	fset := token.NewFileSet()

unix/internal/mkmerge/mkmerge_test.go

@@ -498,7 +498,7 @@ func diffLines(t *testing.T, got, expected []byte) {
 func addLineNr(src []byte) []byte {
 	lines := bytes.Split(src, []byte("\n"))
 	for i, line := range lines {
-		lines[i] = []byte(fmt.Sprintf("%d: %s", i+1, line))
+		lines[i] = fmt.Appendf(nil, "%d: %s", i+1, line)
 	}
 	return bytes.Join(lines, []byte("\n"))
 }