Adding `all' to INTERNAL_MODIFIER_TARGETS to fix `make all'

Commit e334d255 added the `all' pseudo-goal (aka internal modifier
target) to have make dex all Java modules. Unfortunately the new
pseudo-goal wasn't added to INTERNAL_MODIFIER_TARGETS so no actual
phony goal was added, resulting in the obvious

   make: *** No rule to make target `all'.  Stop.

error message when running `make all'. This commit changes
INTERNAL_MODIFIER_TARGETS to also include `all' so that the
pseudo-goal is treated just like `showcommands' and `checkbuild'.

Change-Id: I7905c1e27d1b17bdc1b4331744bf06e18937406f
diff --git a/core/main.mk b/core/main.mk
index b1a54ef..4c772bb 100644
--- a/core/main.mk
+++ b/core/main.mk
@@ -148,7 +148,7 @@
 # These are the modifier targets that don't do anything themselves, but
 # change the behavior of the build.
 # (must be defined before including definitions.make)
-INTERNAL_MODIFIER_TARGETS := showcommands checkbuild
+INTERNAL_MODIFIER_TARGETS := showcommands checkbuild all
 
 # Bring in standard build system definitions.
 include $(BUILD_SYSTEM)/definitions.mk