Revert "DwarfDebug: Pick next location in case of missing location at block begin"

It originally triggered a stepping problem in the debugger, which could
be fixed by adjusting CodeGen/LexicalScopes.cpp however it seems we prefer
the previous behavior anyway.

See the discussion for details: http://lists.llvm.org/pipermail/llvm-commits/Week-of-Mon-20181008/593833.html

This reverts commit r343880.
This reverts commit r343874.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@344318 91177308-0d34-0410-b5e6-96231b3b80d8
8 files changed