MIPS64: ART Vectorizer

MIPS64 implementation which uses MSA extension. Also extended all
relevant checker tests to test MIPS64 implementation.

Test: booted MIPS64R6 in QEMU
Test: ./testrunner.py --target --optimizing -j1 in QEMU

Change-Id: I8b8a2f601076bca1925e21213db8ed1d41d79b52
diff --git a/compiler/optimizing/loop_optimization.h b/compiler/optimizing/loop_optimization.h
index 35298d4..75a42f3 100644
--- a/compiler/optimizing/loop_optimization.h
+++ b/compiler/optimizing/loop_optimization.h
@@ -72,6 +72,7 @@
     kNoUnroundedHAdd = 64,   // no unrounded halving add
     kNoAbs           = 128,  // no absolute value
     kNoMinMax        = 256,  // no min/max
+    kNoStringCharAt  = 512,  // no StringCharAt
   };
 
   /*