Clean up Javac a little bit.

- Added GLOBAL_JAVAC_DEBUG_FLAGS and merge it to
  PRIVATE_JAVACFLAGS/PRIVATE_JACK_FLAGS to get rid of
  PRIVATE_JAVAC_DEBUG_FLAGS/PRIVATE_JACK_DEBUG_FLAGS.
- With Java rules out of base_rules.mk we can get rid
  of java_alternative_checked_module now.

Change-Id: I1a14716c785e3d49330a75044107662ce96a9307
diff --git a/core/host_java_library.mk b/core/host_java_library.mk
index 8ae2e47..0a1119f 100644
--- a/core/host_java_library.mk
+++ b/core/host_java_library.mk
@@ -73,14 +73,12 @@
 full_classes_compiled_jar := $(built_javalib_jar)
 endif # LOCAL_EMMA_INSTRUMENT
 
-$(full_classes_compiled_jar): PRIVATE_JAVAC_DEBUG_FLAGS := -g
-
 # The layers file allows you to enforce a layering between java packages.
 # Run build/tools/java-layers.py for more details.
 layers_file := $(addprefix $(LOCAL_PATH)/, $(LOCAL_JAVA_LAYERS_FILE))
 
 $(full_classes_compiled_jar): PRIVATE_JAVA_LAYERS_FILE := $(layers_file)
-$(full_classes_compiled_jar): PRIVATE_JAVACFLAGS := $(LOCAL_JAVACFLAGS)
+$(full_classes_compiled_jar): PRIVATE_JAVACFLAGS := $(GLOBAL_JAVAC_DEBUG_FLAGS) $(LOCAL_JAVACFLAGS)
 $(full_classes_compiled_jar): PRIVATE_JAR_EXCLUDE_FILES :=
 $(full_classes_compiled_jar): PRIVATE_JAR_PACKAGES :=
 $(full_classes_compiled_jar): PRIVATE_JAR_EXCLUDE_PACKAGES :=