STT: combined build supports more targets to build

The script allows adding more targets using -a option multiple time.
Only a single -a will test aba build as before, but adding multiple
-a options will build the targets in sequence.

Bug: 293821290
Test: combined_build_test.sh -t primary -v userdebug -d out_dist \
                     -a alter1 -a alter2 -a alter3 -c -o -r droid
Change-Id: I3bc4d2f0dad6bac7aa32b165ca667334f90eb83b
1 file changed