Break MDExpression off of DebugNode (inherit directly from `MDNode`) and
drop the fake `DW_TAG_expression` tag in the process.
AFAICT, there's no real functionality change here. The tag was
originally used by `DIDescriptor::isExpression()` to discriminate
between `MDNode`s, but in the new hierarchy we don't need that.
Fixes PR22780.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@232550 91177308-0d34-0410-b5e6-96231b3b80d8
Use definition file for `DW_VIRTUALITY_*`. Add a `DW_VIRTUALITY_max`
both for ease of testing and for future use by the `LLParser`.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@228473 91177308-0d34-0410-b5e6-96231b3b80d8
Also re-implements the `dwarf::Tag` enumerator. I've moved the mock
tags into the enumerator since there's no other way to do this. Really
they shouldn't be used at all (they're just a hack to identify
`MDNode`s, but we have a class hierarchy for that now).
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@228030 91177308-0d34-0410-b5e6-96231b3b80d8
