Moving subprogram specific flags into DISPFlags makes IR code more readable.
In addition, we provide free space in DIFlags for other
'non-subprogram-specific' debug info flags.
Patch by Djordje Todorovic.
Differential Revision: https://reviews.llvm.org/D59288
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@356454 91177308-0d34-0410-b5e6-96231b3b80d8
