[objcopy] Error when --preserve-dates is specified with standard streams

Summary: llvm-objcopy/strip now error when -p is specified when reading from stdin or writing to stdout

Reviewers: jhenderson, rupprecht, espindola, alexshap

Reviewed By: jhenderson, rupprecht

Subscribers: emaste, arichardson, jakehehrlich, MaskRay, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D63090

llvm-svn: 363485