[clang-tidy] Add check misc-multiple-statement-macro

Summary:
The check detects multi-statement macros that are used in unbraced conditionals.
Only the first statement will be part of the conditionals and the rest will fall
outside of it and executed unconditionally.

Reviewers: alexfh

Subscribers: cfe-commits

Differential Revision: http://reviews.llvm.org/D18766

llvm-svn: 266369