Move compile-time asserts to the top-level.

It's still the case that we have many old compilers that can't cope with
anything else ☹.

Change-Id: Ie5a1987cd5164bdbde0c17effaa62aecb7d12352
Reviewed-on: https://boringssl-review.googlesource.com/5320
Reviewed-by: Adam Langley <agl@google.com>
1 file changed