`DISubprogram` combined several fields into a single `spFlags` field in LLVM 8.0

[RyanGlScott]

As of LLVM 8.0, the isLocal, isDefinition, virtuality, and isOptimized fields of DISubprogram have been combined into a single spFlags field. See llvm/llvm-project@adcdc1b. For instance, what used to be displayed as:

!DISubprogram(..., isDefinition: True, isOptimized: True, ...)

Is now displayed as:

!DISubprogram(..., spFlags: DISPFlagDefinition | DISPFlagOptimized, ...)

[RyanGlScott]

At first, I thought that this change in syntax was causing llvm-as to reject the old style. But I was mistaken in that belief: the root cause was actually a separate issue in GaloisInc/llvm-pretty-bc-parser#211. As such, this issue isn't as high of a priority as I originally believed it to be.