ARM64: Introduce TempDoubleRegister as a lithium operand constraint.

src/arm64/lithium-arm64.h

Index: src/arm64/lithium-arm64.h
diff --git a/src/arm64/lithium-arm64.h b/src/arm64/lithium-arm64.h
index f5143ff52e81b1aef88a954db348a177ca83fa89..02cef9066db0773b697ee7329c4793d3bb8c8e0c 100644
--- a/src/arm64/lithium-arm64.h
+++ b/src/arm64/lithium-arm64.h
@@ -3043,6 +3043,9 @@ class LChunkBuilder V8_FINAL : public LChunkBuilderBase {
   // Temporary operand that must be in a register.
   MUST_USE_RESULT LUnallocated* TempRegister();
 
+  // Temporary operand that must be in a double register.
+  MUST_USE_RESULT LUnallocated* TempDoubleRegister();
+
   // Temporary operand that must be in a fixed double register.
   MUST_USE_RESULT LOperand* FixedTemp(DoubleRegister reg);