Revert r108369, sorting llvm.dbg.declare information by source position,

since it doesn't work for front-ends which don't emit column information
(which includes llvm-gcc in its present configuration), and doesn't
work for clang for K&R style variables where the variables are declared
in a different order from the parameter list.

Instead, make a separate pass through the instructions to collect the
llvm.dbg.declare instructions in order. This ensures that the debug
information for variables is emitted in this order.

llvm-svn: 108538