ART: Clean up compiler

Clean up the compiler: less extern functions, dis-entangle
compilers, hide some compiler specifics, lower global includes.

Change-Id: Ibaf88d02505d86994d7845cf0075be5041cc8438
diff --git a/compiler/dex/quick/x86/target_x86.cc b/compiler/dex/quick/x86/target_x86.cc
index 8c6aa5f..604f4bf 100755
--- a/compiler/dex/quick/x86/target_x86.cc
+++ b/compiler/dex/quick/x86/target_x86.cc
@@ -17,6 +17,7 @@
 #include <string>
 #include <inttypes.h>
 
+#include "backend_x86.h"
 #include "codegen_x86.h"
 #include "dex/compiler_internals.h"
 #include "dex/quick/mir_to_lir-inl.h"