Introduce a 'baseline' variant for the compiler.

Implemented as a stripped down version of the optimizing compiler,
not running any optimization.

Adjust code to still work with expectations in code generators.

bug: 111397239

Test: test.py --baseline
Change-Id: I4328283825f9a890616e7496ed4c1e77d6bcc5dd
diff --git a/compiler/optimizing/instruction_simplifier.cc b/compiler/optimizing/instruction_simplifier.cc
index ad50bb8..2b6ae20 100644
--- a/compiler/optimizing/instruction_simplifier.cc
+++ b/compiler/optimizing/instruction_simplifier.cc
@@ -1181,8 +1181,7 @@
   HInstruction* input = instruction->GetInput();
   DataType::Type input_type = input->GetType();
   DataType::Type result_type = instruction->GetResultType();
-  if (DataType::IsTypeConversionImplicit(input_type, result_type)) {
-    // Remove the implicit conversion; this includes conversion to the same type.
+  if (instruction->IsImplicitConversion()) {
     instruction->ReplaceWith(input);
     instruction->GetBlock()->RemoveInstruction(instruction);
     RecordSimplification();