[dsymutil] Upstream update feature.

Now that dsymutil can generate accelerator tables, we can upstream the
update logic that, as the name implies, updates the accelerator tables
in an existing dSYM bundle. In combination with `-minimize` this can be
used to remove redundant .debug_(inlines|pubtypes|pubnames).

Differential revision: https://reviews.llvm.org/D42880

llvm-svn: 324480