[AsmPrinter][DwarfDebug] Skip vars with fragments in different location kinds

The AsmPrinter currently assumes that a Debug Variable will have all of its
fragments with the same "kind" of location (i.e. all in the stack or all in
entry values). This is not enforced by the verifier, so it needs to be handled
properly. Until we do so, we conservatively drop one of the fragments.

Differential Revision: https://reviews.llvm.org/D159468