feat(asm): add LoongArch encoder with ELF and GOOBJ emission

Assisted-by: DeepSeek V4 Pro

verify/groundtruth.go

@@ -32,6 +32,12 @@ func GroundTruthRISCV(path string) (map[string][]byte, error) {
 	return groundTruthArch(path, "riscv64")
 }
 
+// GroundTruthLOONG64 assembles the given .s file with the Go toolchain in
+// LoongArch cross-assembly mode (GOARCH=loong64).
+func GroundTruthLOONG64(path string) (map[string][]byte, error) {
+	return groundTruthArch(path, "loong64")
+}
+
 func groundTruthArch(path, goarch string) (map[string][]byte, error) {
 	goroot := runtime.GOROOT()
 	asmBin := filepath.Join(goroot, "pkg", "tool", runtime.GOOS+"_"+runtime.GOARCH, "asm")
@@ -51,6 +57,7 @@ func groundTruthArch(path, goarch string) (map[string][]byte, error) {
 	pkg := strings.TrimSuffix(base, ".s")
 	pkg = strings.TrimSuffix(pkg, "_amd64")
 	pkg = strings.TrimSuffix(pkg, "_riscv64")
+	pkg = strings.TrimSuffix(pkg, "_loong64")
 
 	cmd := exec.Command(asmBin, "-I", includeDir, "-p", pkg, "-o", objPath, path)
 	if goarch != "" {