Handle negative input in inlined Math.round on Intel CPUs.

src/assembler.h

Index: src/assembler.h
diff --git a/src/assembler.h b/src/assembler.h
index 461bbde2490278cb5e6c3c211ef662645cfe3a4e..06c3b760a60949a5cd30cec77d8e24ae93e51ee4 100644
--- a/src/assembler.h
+++ b/src/assembler.h
@@ -736,6 +736,7 @@ class ExternalReference BASE_EMBEDDED {
   // Static variables containing common double constants.
   static ExternalReference address_of_min_int();
   static ExternalReference address_of_one_half();
+  static ExternalReference address_of_minus_one_half();
   static ExternalReference address_of_minus_zero();
   static ExternalReference address_of_zero();
   static ExternalReference address_of_uint8_max_value();