Rollup merge of #70342 - withoutboats:io-slice-send-sync, r=Mark-Simulacrum

IoSlice/IoSliceMut should be Send and Sync

Closes #70308

src/libstd/io/mod.rs

@@ -951,6 +951,12 @@ fn take(self, limit: u64) -> Take<Self>
 #[repr(transparent)]
 pub struct IoSliceMut<'a>(sys::io::IoSliceMut<'a>);
 
+#[stable(feature = "iovec-send-sync", since = "1.44.0")]
+unsafe impl<'a> Send for IoSliceMut<'a> {}
+
+#[stable(feature = "iovec-send-sync", since = "1.44.0")]
+unsafe impl<'a> Sync for IoSliceMut<'a> {}
+
 #[stable(feature = "iovec", since = "1.36.0")]
 impl<'a> fmt::Debug for IoSliceMut<'a> {
     fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
@@ -1054,6 +1060,12 @@ fn deref_mut(&mut self) -> &mut [u8] {
 #[repr(transparent)]
 pub struct IoSlice<'a>(sys::io::IoSlice<'a>);
 
+#[stable(feature = "iovec-send-sync", since = "1.44.0")]
+unsafe impl<'a> Send for IoSlice<'a> {}
+
+#[stable(feature = "iovec-send-sync", since = "1.44.0")]
+unsafe impl<'a> Sync for IoSlice<'a> {}
+
 #[stable(feature = "iovec", since = "1.36.0")]
 impl<'a> fmt::Debug for IoSlice<'a> {
     fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {