unsupported align size for cl_short16

[Peter Colberg]

luaffi throws an error "unsupported align size" with this definition:

local ffi = require("ffi")
ffi.cdef[[
union cl_short16 {
  short int s[16] __attribute__((aligned(32)));
}
]]

The above works fine with LuaJIT.

[Peter Colberg]

The above error is reproducible with Lua 5.2 and lua-ffi abc638c on Linux x86_64.