[wasm] Add a magic word and a version number to the binary.

src/wasm/wasm-macro-gen.h

Index: src/wasm/wasm-macro-gen.h
diff --git a/src/wasm/wasm-macro-gen.h b/src/wasm/wasm-macro-gen.h
index dd653c174016c9d7c2346b2abba1db8209856a82..7e50d03fd6335563b9a2de5cabf5b5e3bd1a59a8 100644
--- a/src/wasm/wasm-macro-gen.h
+++ b/src/wasm/wasm-macro-gen.h
@@ -265,4 +265,16 @@
 #define WASM_I32_REINTERPRET_F32(x) kExprI32ReinterpretF32, x
 #define WASM_I64_REINTERPRET_F64(x) kExprI64ReinterpretF64, x
 
+#define U32_LE(v)                                    \
+  static_cast<byte>(v), static_cast<byte>((v) >> 8), \
+      static_cast<byte>((v) >> 16), static_cast<byte>((v) >> 24)
+
+#define U16_LE(v) static_cast<byte>(v), static_cast<byte>((v) >> 8)
+
+#define WASM_MODULE_HEADER U32_LE(kWasmMagic), U32_LE(kWasmVersion)
+
+#define SIG_INDEX(v) U16_LE(v)
+#define FUNC_INDEX(v) U16_LE(v)
+#define NAME_OFFSET(v) U32_LE(v)
+
 #endif  // V8_WASM_MACRO_GEN_H_