[esan] Use do-while rather than braces for empty interceptors

Summary:
Replaces {} with a do..while sequence in esan's empty interceptors to allow
natural use with a trailing semicolon.  The sequence uses each argument to
avoid warnings.

Reviewers: filcab

Subscribers: kubabrecka, llvm-commits, zhaoqin

Differential Revision: http://reviews.llvm.org/D19832

llvm-svn: 268426