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