libsigchain: intercept bsd_signal on lp32

bsd_signal is a deprecated synonym for the signal. Nevertheless
there are apps and libraries calling this function.

libsigchain needs to intercept these calls and handle them the same
way it handles signal() call.

Bug: http://b/30562229
Test: readelf --dyn-sym app_process32 and check that bsd_signal is exported
      readelf --dyn-sym app_process64 and check that bsd_signal is not exported
Change-Id: Iec584070b42bc7fa43b114c0f884aff2db5a6858