Add ART_DEFAULT_COMPACT_DEX_LEVEL

If specified, this option changes the default compact dex level used
by dex2oat. Defaults to none currently.

Bug: 63756964
Test: ART_DEFAULT_COMPACT_DEX_LEVEL=fast mm test-art-host-gtest and verify it fails for now.
Test: test/testrunner/testrunner.py --host -j64 and verify it passes

Change-Id: Ib252f432b3545297725656a5cca40d1bb57b0ced
diff --git a/runtime/base/macros.h b/runtime/base/macros.h
index 6cd7d60..512e5ce 100644
--- a/runtime/base/macros.h
+++ b/runtime/base/macros.h
@@ -59,6 +59,10 @@
 #define QUOTE(x) #x
 #define STRINGIFY(x) QUOTE(x)
 
+// Append tokens after evaluating.
+#define APPEND_TOKENS_AFTER_EVAL_2(a, b) a ## b
+#define APPEND_TOKENS_AFTER_EVAL(a, b) APPEND_TOKENS_AFTER_EVAL_2(a, b)
+
 #ifndef NDEBUG
 #define ALWAYS_INLINE
 #else