swift234

Debug Info: Fix a backend crash by removing obsolete linetable heuristics.
Recent versions of LLDB can deal with line 0 locations much better and
due to a subtle bug in the heuristic instructions immediately following
the prologue could end up without debug locations which can cause serious
problems for the LLVM inliner when constructing inline debug scope info.

<rdar://problem/24394944>

(cherry picked from commit 59226f383d61d846943ee6d4335828979af53ce9)