export: wrap exported msgpack symbols

Exporting symbols of a third party library is not a best practice,
as we know from [1]. Let's wrap the msgpack symbols that need to
be exported with the "tnt_" prefix.

While working on the patch, it was decided to export the msgpack
symbols that are used in "msgpuckffi.lua".
In test shared libraries where the symbols "mp_***_{decimal,uuid}"
are used, they are replaced to exported "tnt_mp_***_{decimal,uuid}",
because in the case of linking with "libcore.a" the "libcore.a"
needs to be rebuild with the "-fPIC" flag, that seems as overkill
for tests.

1. https://github.com/tarantool/memcached/issues/59

Closes #5932