Make ART compile with GCC -O0 again.

Tidy up InstructionSetFeatures so that it has a type hierarchy dependent on
architecture.
Add to instruction_set_test to warn when InstructionSetFeatures don't agree
with ones from system properties, AT_HWCAP and /proc/cpuinfo.
Clean-up class linker entry point logic to not return entry points but to
test whether the passed code is the particular entrypoint. This works around
image trampolines that replicate entrypoints.
Bug: 17993736

Change-Id: I5f4b49e88c3b02a79f9bee04f83395146ed7be23
diff --git a/compiler/dex/compiler_ir.h b/compiler/dex/compiler_ir.h
index 37e3a7a..34585c1 100644
--- a/compiler/dex/compiler_ir.h
+++ b/compiler/dex/compiler_ir.h
@@ -68,7 +68,7 @@
   InstructionSet instruction_set;
   bool target64;
 
-  InstructionSetFeatures GetInstructionSetFeatures() {
+  const InstructionSetFeatures* GetInstructionSetFeatures() {
     return compiler_driver->GetInstructionSetFeatures();
   }