[esan|cfrag] Add the skeleton to handle the cfrag argument

Summary:
Adds the struct declaration for the cache-fragmentation tool variable
passed to the runtime library.

Updates test struct-simple.cpp.

Reviewers: aizatsky, bruening

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

Differential Revision: http://reviews.llvm.org/D20542

llvm-svn: 271337