Re-assign registers on ARM so PP and CODE_REG are below R7 (FP on iOS).

runtime/vm/intrinsifier_x64.cc

Index: runtime/vm/intrinsifier_x64.cc
diff --git a/runtime/vm/intrinsifier_x64.cc b/runtime/vm/intrinsifier_x64.cc
index 4598ddd37485a4e06dae9635863ceef0d5f3ee17..93e8521e28f207e5f82bb9af66c109eef1090f95 100644
--- a/runtime/vm/intrinsifier_x64.cc
+++ b/runtime/vm/intrinsifier_x64.cc
@@ -20,12 +20,12 @@ namespace dart {
 DECLARE_FLAG(bool, interpret_irregexp);
 
 // When entering intrinsics code:
-// RBX: IC Data
 // R10: Arguments descriptor
 // TOS: Return address
-// The RBX, R10 registers can be destroyed only if there is no slow-path, i.e.
+// The R10 registers can be destroyed only if there is no slow-path, i.e.
 // if the intrinsified method always executes a return.
 // The RBP register should not be modified, because it is used by the profiler.
+// The PP and THR registers (see constants_x64.h) must be preserved.
 
 #define __ assembler->