PPC: Use aligned buffer for wasm serialization

Fix unaligned memory access error inconstant
pool access during relocation.

Change-Id: I960b59b226cc5f212fff4565b2c7694364f2cb54
Reviewed-on: https://chromium-review.googlesource.com/c/1452357Reviewed-by: Clemens Hammacher <clemensh@chromium.org>
Commit-Queue: Junliang Yan <jyan@ca.ibm.com>
Cr-Commit-Position: refs/heads/master@{#59351}

src/wasm/wasm-serialization.cc

@@ -351,7 +351,8 @@ void NativeModuleSerializer::WriteCode(const WasmCode* code, Writer* writer) {
   writer->WriteVector(code->reloc_info());
   writer->WriteVector(code->source_positions());
   writer->WriteVector(Vector<byte>::cast(code->protected_instructions()));
-#if V8_TARGET_ARCH_MIPS || V8_TARGET_ARCH_MIPS64 || V8_TARGET_ARCH_ARM
+#if V8_TARGET_ARCH_MIPS || V8_TARGET_ARCH_MIPS64 || V8_TARGET_ARCH_ARM || \
+    V8_TARGET_ARCH_PPC
   // On platforms that don't support misaligned word stores, copy to an aligned
   // buffer if necessary so we can relocate the serialized code.
   std::unique_ptr<byte[]> aligned_buffer;