Fix wrong endianness of wasm header in WasmModuleWriter on big-endian platforms

src/wasm/encoder.h

 // Copyright 2015 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef V8_WASM_ENCODER_H_
 #define V8_WASM_ENCODER_H_
 
 #include "src/signature.h"
 #include "src/zone-containers.h"
 
@@ skipping 18 matching lines @@
     end_ = buffer_ + initial;
   }
 
   void write_u8(uint8_t x) {
     EnsureSpace(1);
     *(pos_++) = x;
   }
 
   void write_u16(uint16_t x) {
     EnsureSpace(2);
+#if V8_TARGET_LITTLE_ENDIAN
     WriteUnalignedUInt16(pos_, x);
+#else
+    pos_[0] = x & 0xff;
+    pos_[1] = (x >> 8) & 0xff;
+#endif
     pos_ += 2;
   }
 
   void write_u32(uint32_t x) {
     EnsureSpace(4);
+#if V8_TARGET_LITTLE_ENDIAN
     WriteUnalignedUInt32(pos_, x);
+#else
+    pos_[0] = x & 0xff;
+    pos_[1] = (x >> 8) & 0xff;
+    pos_[2] = (x >> 16) & 0xff;
+    pos_[3] = (x >> 24) & 0xff;
+#endif
     pos_ += 4;
   }
 
   void write_u32v(uint32_t val) {
     EnsureSpace(kMaxVarInt32Size);
     LEBHelper::write_u32v(&pos_, val);
   }
 
   void write_size(size_t val) {
     EnsureSpace(kMaxVarInt32Size);
@@ skipping 163 matching lines @@
   ZoneVector<std::pair<MachineType, bool>> globals_;
   SignatureMap signature_map_;
   int start_function_index_;
 };
 
 }  // namespace wasm
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_WASM_ENCODER_H_