[esan] EfficiencySanitizer libc interceptors

Summary:
Adds libc interceptors to the runtime library for the new
EfficiencySanitizer ("esan") family of tools.  The interceptors cover
the memory operations in most common library calls and will be shared
among all esan tools.

Reviewers: aizatsky

Subscribers: zhaoqin, tberghammer, danalbert, srhines, llvm-commits, vitalybuka, eugenis, kcc

Differential Revision: http://reviews.llvm.org/D19411

llvm-svn: 267293