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/trampolines/trampoline_compiler.cc b/compiler/trampolines/trampoline_compiler.cc
index ac84d6a..d5225c1 100644
--- a/compiler/trampolines/trampoline_compiler.cc
+++ b/compiler/trampolines/trampoline_compiler.cc
@@ -30,11 +30,7 @@
 namespace arm {
 static const std::vector<uint8_t>* CreateTrampoline(EntryPointCallingConvention abi,
                                                     ThreadOffset<4> offset) {
-  // NOTE: the assembler used here is ARM, not Thumb.  This is because the address
-  // returned by this function is a pointer and for thumb we would have to set the
-  // bottom bit.  It doesn't matter since the instructions generated are the same
-  // size anyway.
-  std::unique_ptr<ArmAssembler> assembler(static_cast<ArmAssembler*>(Assembler::Create(kArm)));
+  std::unique_ptr<ArmAssembler> assembler(static_cast<ArmAssembler*>(Assembler::Create(kThumb2)));
 
   switch (abi) {
     case kInterpreterAbi:  // Thread* is first argument (R0) in interpreter ABI.