Bitcode: Prepare to move bitcode readers to free functions.

Make initStream() a free function, and change BitcodeReaderBase ctor to take
a BitstreamCursor.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@286622 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed