convert to SLOT-ed libbase

Also drop CFLAGS setting since it isn't used anywhere.

BUG=chromium-os:16623
TEST=`emerge-x86-alex gestures` still works
TEST=`cros_run_unit_tests --board x86-alex -p gestures` passes

Change-Id: I45bc27f829a1e4fabffaa806cddab4c5c4015c92