Sink DwarfDebug::constructInlinedScopeDIE into DwarfCompileUnit

This introduces access to the AbstractSPDies map from DwarfDebug so
DwarfCompileUnit can access it. Eventually this'll sink down to
DwarfFile, but it'll still be generically accessible - not much
encapsulation to provide it. (constructInlinedScopeDIE could stay
further up, in DwarfFile to avoid exposing this - but I don't think
that's particularly better)

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@219411 91177308-0d34-0410-b5e6-96231b3b80d8