Rollup merge of #82228 - ijackson:nonzero-cint, r=KodrAus

Provide NonZero_c_* integers

I'm pretty sure I am going want this for #73125 and it seems like an
omission that would be in any case good to remedy.

<strike>Because the raw C types are in `std`, not `core`, to achieve this we
must export the relevant macros from `core` so that `std` can use
them.  That's done with a new `num_internals` perma-unstable feature.

The macros need to take more parameters for the module to get the
types from and feature attributes to use.

I have eyeballed the docs output for core, to check that my changes to
these macros have made no difference to the core docs output.</strike>

library/std/src/lib.rs

@@ -263,6 +263,7 @@
 #![feature(exact_size_is_empty)]
 #![feature(exhaustive_patterns)]
 #![feature(extend_one)]
+#![feature(extended_key_value_attributes)]
 #![feature(external_doc)]
 #![feature(fn_traits)]
 #![feature(format_args_nl)]