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 surfaceflinger and check that bsd_signal is exported for lp32
      and is not exported for lp64 binary version
Change-Id: If80e45502275b26c3ee4026ab12cadd77f8fbd3b