fix: staticcheck and deadcode findings repo-wide, modernize counting loops

verify/groundtruth.go

@@ -38,6 +38,17 @@ func GroundTruthLOONG64(path string) (map[string][]byte, error) {
 	return groundTruthArch(path, "loong64")
 }
 
+// goRoot locates the GOROOT of the `go` binary on PATH: the build-time
+// runtime.GOROOT is meaningless for a relocated binary, so the toolchain is
+// asked directly.
+func goRoot() (string, error) {
+	out, err := exec.Command("go", "env", "GOROOT").Output()
+	if err != nil {
+		return "", fmt.Errorf("verify: go env GOROOT: %w", err)
+	}
+	return strings.TrimSpace(string(out)), nil
+}
+
 // GroundTruthARM64 assembles the given .s file with the Go toolchain in
 // AArch64 cross-assembly mode (GOARCH=arm64).
 func GroundTruthARM64(path string) (map[string][]byte, error) {
@@ -45,7 +56,10 @@ func GroundTruthARM64(path string) (map[string][]byte, error) {
 }
 
 func groundTruthArch(path, goarch string) (map[string][]byte, error) {
-	goroot := runtime.GOROOT()
+	goroot, err := goRoot()
+	if err != nil {
+		return nil, err
+	}
 	asmBin := filepath.Join(goroot, "pkg", "tool", runtime.GOOS+"_"+runtime.GOARCH, "asm")
 	if _, err := os.Stat(asmBin); err != nil {
 		return nil, fmt.Errorf("verify: go tool asm not found at %s: %w", asmBin, err)