[DebugInfo] IR/Bitcode changes for DISubprogram flags.

Packing the flags into one bitcode word will save effort in
adding new flags in the future.

Differential Revision: https://reviews.llvm.org/D54755

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@347806 91177308-0d34-0410-b5e6-96231b3b80d8
19 files changed