[Remarks] Retain all remarks by default, add option to drop without DL.

[Remarks] Retain all remarks by default, add option to drop without DL.

At the moment, dsymutil drops all remarks without debug location.

There are many cases where debug location may be missing for remarks,
mostly due LLVM not preserving debug locations. When using bitstream
remarks for statistical analysis, those missed remarks mean we get an
incomplete picture.

The patch flips the default to keeping all remarks and leaving it to
tools that display remarks to filter out remarks without debug locations
as needed.

The new --remarks-drop-without-debug flag can be used to drop remarks
without debug locations, i.e. restore the previous behavior.

Reviewed By: thegameg

Differential Revision: https://reviews.llvm.org/D151089