Write legacy function attributes properly.

Bug: 9503142

A prior LLVM rebase accidentally overwrote the various bitcode writer
implementations with respect to function attributes. They were writing a new
style section, which would not be able to be parsed/used on older devices.
This change restores the generation of the legacy function attribute bitcode
format.

Change-Id: Ib6afc5ae405303881605c51c34b6966e4754c29d
7 files changed