Add `WRAPPED_CTASSERT` macro by annotating CTASSERTs with __unused
to deal with -Wunused-local-typedefs warnings from gcc 4.8+.
All other compilers (clang, etc) use CTASSERT as-is. A more generic
solution for this issue will be proposed after ^/stable/11 is forked.
Consolidate all CTASSERTs under one block instead of inlining them in
functions.