Ensure libidmap2 exists for all ABIs

The build process doesn't produce the libidmap2 for 32-bit by default.
Android Resources SelfTargeting requires libidmap2. This patch makes
libidmap2 into both 32-bit and 64-bit libraries.

Fixes: 205919743
Test: lunch <device>-userdebug; make clean; make ;\
      test -f $ANDROID_PRODUCT_OUT/system/lib/libidmap2.so \
      && echo 32-bit libidmap2.so exists
Change-Id: Ia1d0338be1416cc3510246737910d2371d2a9e04