[llvm-size] print a blank line between archieve members when using sysv format

Summary: This patch is related to https://bugs.llvm.org/show_bug.cgi?id=42967 and it fixes llvm-size's sysv format output by adding a blank line between archieve members

Reviewers: jhenderson, Jim, MaskRay

Reviewed By: jhenderson, Jim, MaskRay

Subscribers: MaskRay, Jim, rupprecht, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D71957