[Liftoff][arm64] Use wzr/xzr for spilling zero constants

This removes a redundant "mov <reg>, #0" by spilling the zero register
directly.

Change-Id: I608f5200ee25e176f6d3279aec07c581d9f7d769
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1517872Reviewed-by: Clemens Hammacher <clemensh@chromium.org>
Commit-Queue: Martyn Capewell <martyn.capewell@arm.com>
Cr-Commit-Position: refs/heads/master@{#60192}

src/wasm/baseline/arm64/liftoff-assembler-arm64.h

@@ -345,12 +345,20 @@ void LiftoffAssembler::Spill(uint32_t index, WasmValue value) {
   CPURegister src = CPURegister::no_reg();
   switch (value.type()) {
     case kWasmI32:
-      src = temps.AcquireW();
-      Mov(src.W(), value.to_i32());
+      if (value.to_i32() == 0) {
+        src = wzr;
+      } else {
+        src = temps.AcquireW();
+        Mov(src.W(), value.to_i32());
+      }
       break;
     case kWasmI64:
-      src = temps.AcquireX();
-      Mov(src.X(), value.to_i64());
+      if (value.to_i64() == 0) {
+        src = xzr;
+      } else {
+        src = temps.AcquireX();
+        Mov(src.X(), value.to_i64());
+      }
       break;
     default:
       // We do not track f32 and f64 constants, hence they are unreachable.