Base: Explicitly set abort message on FATAL

Currently bionic only stores the first invocation of
android_set_abort_message, libbase splits the logging invocations
into discrete lines, and liblog automatically calls bionic when
fatal severity is used. This leads to only the first line of
LOG(FATAL) being stored for tombstoned.

Eagerly set the abort message directly before logging when the
severity is FATAL. This ensures the complete message will be
available.

Bug: 120506942
Test: m
Test: manual
Change-Id: I104d6960a2b1f66f21f5ada383fb4ab0f35e96a9