Move trampolines to thumb2 instead of ARM

Currently the entrypoint trampolines are compiled using the ARM32 assembler.
This changes that to use the thumb2 assembler for consistency with the
other compiled code.

Bug: 15455279
Change-Id: I6bacdf359e2ae4c0967fb5cd9dc694af11f802ec
diff --git a/compiler/compiled_method.h b/compiler/compiled_method.h
index 23cd250..b8cd851 100644
--- a/compiler/compiled_method.h
+++ b/compiler/compiled_method.h
@@ -67,6 +67,7 @@
   // returns the difference between the code address and a usable PC.
   // mainly to cope with kThumb2 where the lower bit must be set.
   size_t CodeDelta() const;
+  static size_t CodeDelta(InstructionSet instruction_set);
 
   // Returns a pointer suitable for invoking the code at the argument
   // code_pointer address.  Mainly to cope with kThumb2 where the