Create an internal prelude

When building with `rustc-dep-of-std`, we don't get the core types
imported by default (`Clone`, `Copy`, `Option`). In order to avoid
needing to import these individually, introduce a prelude that includes
them.

This also includes the C numeric types that are frequently used.

src/lib.rs

@@ -36,8 +36,6 @@ cfg_if! {
         use core::iter;
         #[allow(unused_imports)]
         use core::ops;
-        #[allow(unused_imports)]
-        use core::option;
     }
 }
 
@@ -62,6 +60,17 @@ use core::num;
 #[allow(unused_imports)]
 use core::option::Option;
 
+/// Frequently-used types that are available on all platforms
+///
+/// We need to reexport the core types so this works with `rust-dep-of-std`.
+mod prelude {
+    #[allow(unused_imports)]
+    pub(crate) use crate::{
+        c_char, c_int, c_long, c_longlong, c_short, c_uchar, c_uint, c_ulong, c_ulonglong,
+        c_ushort, c_void, intptr_t, size_t, ssize_t, Clone, Copy, Option,
+    };
+}
+
 cfg_if! {
     if #[cfg(windows)] {
         mod fixed_width_ints;