Move hash code from hidden string to a private symbol

src/mips64/macro-assembler-mips64.cc

Index: src/mips64/macro-assembler-mips64.cc
diff --git a/src/mips64/macro-assembler-mips64.cc b/src/mips64/macro-assembler-mips64.cc
index 154276672216da103507f4a92f2ad689bde09ac8..31b35d7cf10bdb75b2b6b2ce4179dbc22feb6d59 100644
--- a/src/mips64/macro-assembler-mips64.cc
+++ b/src/mips64/macro-assembler-mips64.cc
@@ -528,6 +528,7 @@ void MacroAssembler::GetNumberHash(Register reg0, Register scratch) {
   // hash = hash ^ (hash >> 16);
   srl(at, reg0, 16);
   xor_(reg0, reg0, at);
+  And(reg0, reg0, Operand(0x3fffffff));
 }