[DebugInfo] DISubprogram flags get their own flags word. NFC.
This will hold flags specific to subprograms. In the future
we could potentially free up scarce bits in DIFlags by moving
subprogram-specific flags from there to the new flags word.

This patch does not change IR/bitcode formats, that will be
done in a follow-up.

Differential Revision: https://reviews.llvm.org/D54597

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@347239 91177308-0d34-0410-b5e6-96231b3b80d8
16 files changed