[clang] Replacing asserts with static_asserts where appropriate

Summary: This patch consists of the suggestions of clang-tidy/misc-static-assert check.

Reviewers: alexfh

Subscribers: dblaikie, xazax.hun, cfe-commits

Differential Revision: http://reviews.llvm.org/D8344

Patch by Szabolcs Sipos!

llvm-svn: 232367