ART: Some Quick cleanup

Make several fields const in CompilationUnit. May benefit some Mir2Lir
code that repeats tests, and in general immutability is good.

Remove compiler_internals.h and refactor some other headers to reduce
overly broad imports (and thus forced recompiles on changes).

Change-Id: I898405907c68923581373b5981d8a85d2e5d185a
diff --git a/compiler/dex/local_value_numbering_test.cc b/compiler/dex/local_value_numbering_test.cc
index 0fcb584..c894892 100644
--- a/compiler/dex/local_value_numbering_test.cc
+++ b/compiler/dex/local_value_numbering_test.cc
@@ -14,7 +14,6 @@
  * limitations under the License.
  */
 
-#include "compiler_internals.h"
 #include "dex/mir_field_info.h"
 #include "global_value_numbering.h"
 #include "local_value_numbering.h"
@@ -202,7 +201,7 @@
 
   LocalValueNumberingTest()
       : pool_(),
-        cu_(&pool_),
+        cu_(&pool_, kRuntimeISA, nullptr, nullptr),
         mir_count_(0u),
         mirs_(nullptr),
         ssa_reps_(),