feat(riscv64): GOROOT instruction shapes, DATA order and offset expressions

Assisted-by: GLM 5.3 Flash

cmd/gasm/main.go

@@ -511,8 +511,10 @@ requires -p, the package path, and the installed Go toolchain).
 		fmt.Fprintf(os.Stderr, "%s: %v\n", path, err)
 		return 1
 	}
-	if len(img.Funcs) == 0 {
-		fmt.Fprintln(os.Stderr, "gasm asm: no assemblable TEXT functions found")
+	if len(img.Funcs) == 0 && len(img.Data) == 0 {
+		// A file with neither code nor data assembles to nothing, which is
+		// almost always a wrong architecture rather than an intent.
+		fmt.Fprintln(os.Stderr, "gasm asm: no assemblable TEXT functions or GLOBL data found")
 		return 1
 	}
 	for _, fn := range img.Funcs {