Fix wasm32v1-none compilation errors

- arrayvec.rs: Use concrete return types ([T], slice::Iter, slice::IterMut)
  instead of Self::Target/Self::IntoIter to avoid E0223 ambiguity
  introduced by the Receiver trait in Rust 1.87+
- char.rs: Explicitly import Result/Ok/Err from core for target_os=none
  where the standard prelude is not auto-injected

benches/extend.rs

@@ -0,0 +1,78 @@
+
+extern crate arrayvec;
+#[macro_use] extern crate bencher;
+
+use std::io::Write;
+
+use arrayvec::ArrayVec;
+
+use bencher::Bencher;
+use bencher::black_box;
+
+fn extend_with_constant(b: &mut Bencher) {
+    let mut v = ArrayVec::<u8, 512>::new();
+    let cap = v.capacity();
+    b.iter(|| {
+        v.clear();
+        let constant = black_box(1);
+        v.extend((0..cap).map(move |_| constant));
+        v[511]
+    });
+    b.bytes = v.capacity() as u64;
+}
+
+fn extend_with_range(b: &mut Bencher) {
+    let mut v = ArrayVec::<u8, 512>::new();
+    let cap = v.capacity();
+    b.iter(|| {
+        v.clear();
+        let range = 0..cap;
+        v.extend(range.map(|x| black_box(x as _)));
+        v[511]
+    });
+    b.bytes = v.capacity() as u64;
+}
+
+fn extend_with_slice(b: &mut Bencher) {
+    let mut v = ArrayVec::<u8, 512>::new();
+    let data = [1; 512];
+    b.iter(|| {
+        v.clear();
+        let iter = data.iter().map(|&x| x);
+        v.extend(iter);
+        v[511]
+    });
+    b.bytes = v.capacity() as u64;
+}
+
+fn extend_with_write(b: &mut Bencher) {
+    let mut v = ArrayVec::<u8, 512>::new();
+    let data = [1; 512];
+    b.iter(|| {
+        v.clear();
+        v.write(&data[..]).ok();
+        v[511]
+    });
+    b.bytes = v.capacity() as u64;
+}
+
+fn extend_from_slice(b: &mut Bencher) {
+    let mut v = ArrayVec::<u8, 512>::new();
+    let data = [1; 512];
+    b.iter(|| {
+        v.clear();
+        v.try_extend_from_slice(&data).ok();
+        v[511]
+    });
+    b.bytes = v.capacity() as u64;
+}
+
+benchmark_group!(benches,
+                 extend_with_constant,
+                 extend_with_range,
+                 extend_with_slice,
+                 extend_with_write,
+                 extend_from_slice
+);
+
+benchmark_main!(benches);