Add support for generating a dsymutil reproducer. The result is a folder
containing all the object files for linking.
When --gen-reproducer is passed, dsymutil uses a FileCollectorFileSystem
which keeps track of all the files used by dsymutil. These files are
copied into a temporary directory when dsymutil exists.
When this path is passed to --use-reproducer, dsymutil uses a
RedirectingFileSystem that will use the files from the reproducer
directory instead of the actual paths. This means you don't need to mess
with the OSO path prefix.
Differential revision: https://reviews.llvm.org/D79398
Jonas Devlieghere