Fix math min/max for -0.0 case. Enable min_max_test to run in optimizing compiler as well.

runtime/vm/constants_mips.h

Index: runtime/vm/constants_mips.h
===================================================================
--- runtime/vm/constants_mips.h	(revision 25288)
+++ runtime/vm/constants_mips.h	(working copy)
@@ -155,6 +155,14 @@
   kNoDRegister = -1,
 };
 
+static inline FRegister EvenFRegisterOf(DRegister d) {
+  return static_cast<FRegister>(d * 2);
+}
+
+static inline FRegister OddFRegisterOf(DRegister d) {
+  return static_cast<FRegister>((d * 2) + 1);
+}
+
 const DRegister DTMP = D9;
 const FRegister STMP1 = F18;
 const FRegister STMP2 = F19;