Fix the way the ShouldStopHere checker handles the general case of "stepping...

Fix the way the ShouldStopHere checker handles the general case of "stepping through line 0 code".  
That's good 'cause it means all the different kinds of source line stepping won't leave user in the middle of
compiler implementation code or code inlined from odd places, etc.  But it turns out that the compiler
also marks functions it MIGHT inline as all being of line 0.  That would mean we single step through this code
instead of just stepping out.  That is both inefficient, and more error prone 'cause these little nuggets tend
to be bits of hand-written assembly and the like and are hard to step through.

This change just checks and if the entire function is marked with line 0, we step out rather than step through.

<rdar://problem/25966460>

llvm-svn: 268823