Implement isNaN intrinsic through HIR equivalent.

Rationale:
Efficient implementation on all platforms.
Subject to better compiler optimizations.

Change-Id: Ie8876bf5943cbe1138491a25d32ee9fee554043c
diff --git a/compiler/optimizing/intrinsics_mips.cc b/compiler/optimizing/intrinsics_mips.cc
index 2294713..e93b939 100644
--- a/compiler/optimizing/intrinsics_mips.cc
+++ b/compiler/optimizing/intrinsics_mips.cc
@@ -1016,8 +1016,6 @@
 
 UNIMPLEMENTED_INTRINSIC(FloatIsInfinite)
 UNIMPLEMENTED_INTRINSIC(DoubleIsInfinite)
-UNIMPLEMENTED_INTRINSIC(FloatIsNaN)
-UNIMPLEMENTED_INTRINSIC(DoubleIsNaN)
 
 UNIMPLEMENTED_INTRINSIC(IntegerHighestOneBit)
 UNIMPLEMENTED_INTRINSIC(LongHighestOneBit)
@@ -1025,6 +1023,8 @@
 UNIMPLEMENTED_INTRINSIC(LongLowestOneBit)
 
 // Handled as HIR instructions.
+UNIMPLEMENTED_INTRINSIC(FloatIsNaN)
+UNIMPLEMENTED_INTRINSIC(DoubleIsNaN)
 UNIMPLEMENTED_INTRINSIC(IntegerCompare)
 UNIMPLEMENTED_INTRINSIC(LongCompare)
 UNIMPLEMENTED_INTRINSIC(IntegerSignum)