add repr(transparent) to IoSliceMut where missing

Author: nivkner

src/libstd/sys/unix/io.rs

@@ -29,6 +29,7 @@ impl<'a> IoSlice<'a> {
     }
 }
 
+#[repr(transparent)]
 pub struct IoSliceMut<'a> {
     vec: iovec,
     _p: PhantomData<&'a mut [u8]>,

src/libstd/sys/wasi/io.rs

@@ -29,6 +29,7 @@ impl<'a> IoSlice<'a> {
     }
 }
 
+#[repr(transparent)]
 pub struct IoSliceMut<'a> {
     vec: __wasi_iovec_t,
     _p: PhantomData<&'a mut [u8]>,

src/libstd/sys/windows/io.rs

@@ -29,6 +29,7 @@ impl<'a> IoSlice<'a> {
     }
 }
 
+#[repr(transparent)]
 pub struct IoSliceMut<'a> {
     vec: c::WSABUF,
     _p: PhantomData<&'a mut [u8]>,