COFF: Implement /linkrepro flag.

This flag is implemented similarly to --reproduce in the ELF linker.

This patch implements /linkrepro by moving the cpio writer and associated
utility functions to lldCore, and using that implementation in both linkers.

One COFF-specific detail is that we store the object file from which the
resource files were created in our reproducer, rather than the resource
files themselves. This allows the reproducer to be used on non-Windows
systems for example.

Differential Revision: https://reviews.llvm.org/D22418

llvm-svn: 276719