Fix typos

src/libcore/cell.rs

@@ -492,7 +492,7 @@ impl<T: ?Sized> Cell<T> {
     #[inline]
     #[stable(feature = "cell_get_mut", since = "1.11.0")]
     pub fn get_mut(&mut self) -> &mut T {
-        // SAFETY: not threadsafe, but it's OK since we know C`ell` isn't threadsafe
+        // SAFETY: not threadsafe, but it's OK since we know `Cell` isn't threadsafe
         unsafe {
             &mut *self.value.get()
         }

src/libcore/str/mod.rs

@@ -1130,7 +1130,7 @@ impl<'a, P: Pattern<'a>> SplitInternal<'a, P> {
                 self.end = a;
                 Some(elt)
             },
-            // SAFETY: `self.start` and `self.end` always lie on unicode boudaries
+            // SAFETY: `self.start` and `self.end` always lie on unicode boundaries
             None => unsafe {
                 self.finished = true;
                 Some(haystack.get_unchecked(self.start..self.end))