global init must have correct type

[redianthus]

On the ray tracer bench:

$ ...
global init must have correct type, on
(struct.new $BlockFloat_3
 (i32.const 3)
 (f64.const 0)
 (f64.const 0)
 (f64.const 0)
)

(type $BlockFloat_3 (sub $BlockFloat_2 (struct (field (mut i16)) (field (mut f64)) (field (mut f64)) (field (mut f64)))))

;; ...
(global $camlRaytrace__Pmakearray_5411 (export "camlRaytrace__Pmakearray_5411") (ref $BlockFloat_3) (struct.new $BlockFloat_3 (i32.const 3) (f64.const 0x0p+0) (f64.const 0x0p+0) (f64.const 0x0p+0)))