The Bitstream part of Bitcode moved to llvm/Bitstream in LLVM. This
updates the uses in swift.
See r365091 [Bitcode] Move Bitstream to a separate library.
(cherry picked from commit 1cd8e19357)
* Fix Swift following bitstream reader API update
Upstream change in rL364464 broke downstream Swift.
(cherry picked from commit 50de105bf1)
Conflicts:
lib/Serialization/Deserialization.cpp
lib/Serialization/ModuleFile.cpp
tools/driver/modulewrap_main.cpp