[DWARF] Fix a bug in line info handling

[DWARF] Fix a bug in line info handling

This fixes a bug in the line info handling in the dwarf code, based on a
problem I when implementing RelocVisitor support for MachO.
Since addr+size will give the first address past the end of the function,
we need to back up one line table entry. Fix this by looking up the
end_addr-1, which is the last address in the range. Note that this also
removes a duplicate output from the llvm-rtdyld line table dump. The
relevant line is the end_sequence one in the line table and has an offset
of the first address part the end of the range and hence should not be
included.
Also factor out the common functionality into a separate function.
This comes up on MachO much more than on ELF, since MachO
doesn't store the symbol size separately, hence making
said situation always occur.

Differential Revision: http://reviews.llvm.org/D9925

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@238699 91177308-0d34-0410-b5e6-96231b3b80d8