ARM: Add new String.compareTo intrinsic.

Benchmarked on Nexus6P big, little, and all cores. The new intrinsic is
faster than pStringCompareTo for compare lengths on [1,512], so the
runtime call is no longer needed.

Change-Id: If853b592dfc5e561ea3389b51729f37a2c89c18e
diff --git a/runtime/arch/arm/entrypoints_init_arm.cc b/runtime/arch/arm/entrypoints_init_arm.cc
index f0e9ac5..4c68862 100644
--- a/runtime/arch/arm/entrypoints_init_arm.cc
+++ b/runtime/arch/arm/entrypoints_init_arm.cc
@@ -97,7 +97,8 @@
 
   // Intrinsics
   qpoints->pIndexOf = art_quick_indexof;
-  qpoints->pStringCompareTo = art_quick_string_compareto;
+  // The ARM StringCompareTo intrinsic does not call the runtime.
+  qpoints->pStringCompareTo = nullptr;
   qpoints->pMemcpy = memcpy;
 
   // Read barrier.