Recommit r288212: Emit 'no line' information for interesting 'orphan' instructions.

DWARF specifies that "line 0" really means "no appropriate source
location" in the line table.  By default, use this for branch targets
and some other cases that have no specified source location, to
prevent inheriting unfortunate line numbers from physically preceding
instructions (which might be from completely unrelated source).

Updated patch allows enabling or suppressing this behavior for all
unspecified source locations.

Differential Revision: http://reviews.llvm.org/D24180

llvm-svn: 289468