Use slice::iter instead of into_iter to avoid future breakage

`an_array.into_iter()` currently just works because of the autoref
feature, which then calls `<[T] as IntoIterator>::into_iter`. But
in the future, arrays will implement `IntoIterator`, too. In order
to avoid problems in the future, the call is replaced by `iter()`
which is shorter and more explicit.

Author: LukasKalbertodt

build.rs

@@ -9,7 +9,7 @@ fn main() {
     let force_spin_cfg = is_var_set("CARGO_CFG_LAZY_STATIC_SPIN_IMPL");
 
     let impls_forced = [force_heap_cfg, force_inline_cfg, force_spin_cfg]
-        .into_iter()
+        .iter()
         .filter(|&&f| f)
         .count();