[esan|cfrag] Add test struct-simple.cpp

Summary: Adds a new test struct-simple.cpp for testing the
cache-fragmentation tool with a multi-compilation-unit application.

Patch by Qin Zhao.

Reviewers: bruening

Subscribers: kubabrecka, kcc, vitalybuka, eugenis, aizatsky, llvm-commits, zhaoqin

Differential Revision: http://reviews.llvm.org/D20599

llvm-svn: 270631