[DebugInfo] Print non-verbose output at some point as verbose output

Verbose and non-verbose parsing of .debug_line produced their output at
different points in the program. The most obvious impact of this was
that error messages were produced at different times, but it also
potentially reduced what clients could do by customising the stream or
warning/error handlers.

This change makes the two variants consistent by printing non-verbose
output inline, the same as verbose output.

Testing of the error messages has been modified to check the messages
always appear in the same location to illustrate the behaviour.

Reviewed by: JDevlieghere, dblaikie, MaskRay, labath

Differential Revision: https://reviews.llvm.org/D80989