Change CodeGen to use .loc directives. This produces a lot more readable output

Change CodeGen to use .loc directives. This produces a lot more readable output
and testing is easier.  A good example is the unknown-location.ll test that
now can just look for ".loc 1 0 0".  We also don't use a DW_LNE_set_address for
every address change anymore.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@119613 91177308-0d34-0410-b5e6-96231b3b80d8