Implement
https://blueprints.launchpad.net/tarantool/+spec/consistent-header-guards

Audit all header files in tarantool code base for consistent use
of header guards:
- consistent naming scheme, following doc/coding-style.txt
- header guard goes before the copyright
- each header is self-sufficient.
- add copyright headers where they were missing.

Remove __packed__, __unused__, __noinline__ and __regparm2__ from util.h,
since the name __unused__ conflicted with a parameter name in
third_party/valgrind/valrgind.h, which led to a dependency in inclusion
order between util.h and this header. The define names were not standard, I
couldn't come up with some meaningful and standard names, and they were only
saving some typing, while not providing any extra functionality.