MIPS: Fix bug in StringConstructCode builtin.

src/mips/builtins-mips.cc

Index: src/mips/builtins-mips.cc
diff --git a/src/mips/builtins-mips.cc b/src/mips/builtins-mips.cc
old mode 100644
new mode 100755
index fd35a35588195ac62d2f312095a0ba3ed30e3734..35d21f05e65cda706ed1aa31013cd8103654dc1d
--- a/src/mips/builtins-mips.cc
+++ b/src/mips/builtins-mips.cc
@@ -273,7 +273,7 @@ void Builtins::Generate_StringConstructCode(MacroAssembler* masm) {
   __ IncrementCounter(counters->string_ctor_conversions(), 1, a3, t0);
   {
     FrameScope scope(masm, StackFrame::INTERNAL);
-    __ push(v0);
+    __ push(a0);
     __ InvokeBuiltin(Builtins::TO_STRING, CALL_FUNCTION);
   }
   __ pop(function);