libcdecl: Avoid overalignment of string tables.

libcdecl: Avoid overalignment of string tables.

For whatever reason, on x86_64 gcc allocates any static array at least
32 bytes in size with 32 byte alignment.  In the case of things like
constant string tables, this ends up wasting a bunch of space for no
obvious reason.

Adding suitable _Alignas directives works to prevent overalignment.