[clang-tidy] Assert related checkers

This patch contains two assert related checkers. These checkers are the part of
those that is being open sourced by Ericsson
(http://lists.cs.uiuc.edu/pipermail/cfe-dev/2014-December/040520.html).

The checkers:

AssertSideEffect:
/// \brief Finds \c assert() with side effect.
///
/// The conition of \c assert() is evaluated only in debug builds so a condition
/// with side effect can cause different behaviour in debug / relesase builds.

StaticAssert:
/// \brief Replaces \c assert() with \c static_assert() if the condition is 
/// evaluatable at compile time.
///
/// The condition of \c static_assert() is evaluated at compile time which is
/// safer and more efficient.

http://reviews.llvm.org/D7375

Patch by Szabolcs Sipos!

llvm-svn: 230943