Inline empty constructor.
Fix accidental fallthrough in DebugLocEntry::hasSameValueOrLocation

No test case (this would invoke UB by examining uninitialized members,
etc, at best - and this code is apparently untested anyway - I'm about
to fix that)

Code review feedback from Adrian Prantl on r205360.
Partially revert r204517 and fix a different way:

We don't want to encourage the code to emit a lexical block for
a function that needs one in order for the line table to change,
we need to grab the line information from the body of the pattern
that we were instantiated from, this code should do that.

Modify the test case to ensure that we're still looking in the
right place for all of the scopes and also that we haven't
created a lexical block where we didn't need one.