[esan][cfrag] Add skeleton for cache fragmentation tool support

Summary:
Adds cache_frag.h and cache_frag.cpp for the cache fragmentation tool.

Updates test struct-simple.cpp.

Reviewers: aizatsky

Subscribers: filcab, zhaoqin, llvm-commits, eugenis, vitalybuka, kcc, bruening, kubabrecka

Differential Revision: http://reviews.llvm.org/D20538

llvm-svn: 270737