Sort out ANDROID_GOALS, KATI_GOALS and NINJA_GOALS.

ANDROID_GOALS: any Android goals that need to be built.
KATI_GOALS: goals that we need to pass to Kati.
NINJA_GOALS: goals we need to pass to Ninja.

For modifier Android goals (dist, INTERNAL_MODIFIER_TARGETS),
we don't need to pass them to Ninja. See also commit
80e46c7c5cb7b1d80114876d301798a8624b4200.
Restore the dist rule removed by the above commit.

Previously "droid" was never passed to Ninja. That's incorrect.
"make droid docs" should build both docs and droiod.
Fixed with this change.

Change-Id: I5c28061fe0ebe7848872ee349056d029b787ff71
diff --git a/core/distdir.mk b/core/distdir.mk
index 24beddc..51ec46e 100644
--- a/core/distdir.mk
+++ b/core/distdir.mk
@@ -22,6 +22,11 @@
 
 dist_goal := $(strip $(filter dist,$(MAKECMDGOALS)))
 MAKECMDGOALS := $(strip $(filter-out dist,$(MAKECMDGOALS)))
+ifeq (,$(strip $(filter-out $(INTERNAL_MODIFIER_TARGETS),$(MAKECMDGOALS))))
+# The commandline was something like "make dist" or "make dist showcommands".
+# Add a dependency on a real target.
+dist: $(DEFAULT_GOAL)
+endif
 
 ifdef dist_goal