Include a list of all built-in language items

[Havvy]

From language items: "The set of language items is currently considered unstable. A complete list of the built-in language items will be added in the future."

[Havvy]

This is a list of all lang items and which file they are located in as of this comment.

src/libstd/f32.rs:#[lang = "f32"]
src/libstd/panicking.rs:#[lang = "panic_fmt"]
src/libstd/f64.rs:#[lang = "f64"]
src/libstd/rt.rs:#[lang = "start"]
src/libstd_unicode/char.rs:#[lang = "char"]
src/libpanic_unwind/emcc.rs:#[lang = "eh_personality"]
src/libpanic_unwind/seh64_gnu.rs:#[lang = "eh_personality"]
src/libpanic_unwind/seh64_gnu.rs:#[lang = "eh_unwind_resume"]
src/libpanic_unwind/seh.rs:#[cfg_attr(not(test), lang = "msvc_try_filter")]
src/libpanic_unwind/seh.rs:#[lang = "eh_personality"]
src/libpanic_unwind/gcc.rs:#[lang = "eh_unwind_resume"]
src/liballoc/boxed.rs:#[lang = "owned_box"]
src/liballoc/slice.rs:#[lang = "slice"]
src/liballoc/str.rs:#[lang = "str"]
src/liballoc/heap.rs:#[lang = "exchange_malloc"]
src/liballoc/heap.rs:#[cfg_attr(not(test), lang = "box_free")]
src/libcore/ops/unsize.rs:#[lang = "coerce_unsized"]
src/libcore/ops/bit.rs:#[lang = "not"]
src/libcore/ops/bit.rs:#[lang = "bitand"]
src/libcore/ops/bit.rs:#[lang = "bitor"]
src/libcore/ops/bit.rs:#[lang = "bitxor"]
src/libcore/ops/bit.rs:#[lang = "shl"]
src/libcore/ops/bit.rs:#[lang = "shr"]
src/libcore/ops/bit.rs:#[lang = "bitand_assign"]
src/libcore/ops/bit.rs:#[lang = "bitor_assign"]
src/libcore/ops/bit.rs:#[lang = "bitxor_assign"]
src/libcore/ops/bit.rs:#[lang = "shl_assign"]
src/libcore/ops/bit.rs:#[lang = "shr_assign"]
src/libcore/ops/deref.rs:#[lang = "deref"]
src/libcore/ops/deref.rs:#[lang = "deref_mut"]
src/libcore/ops/index.rs:#[lang = "index"]
src/libcore/ops/index.rs:#[lang = "index_mut"]
src/libcore/ops/generator.rs:#[cfg_attr(not(stage0), lang = "generator_state")]
src/libcore/ops/generator.rs:#[cfg_attr(not(stage0), lang = "generator")]
src/libcore/ops/drop.rs:#[lang = "drop"]
src/libcore/ops/function.rs:#[lang = "fn"]
src/libcore/ops/function.rs:#[lang = "fn_mut"]
src/libcore/ops/function.rs:#[lang = "fn_once"]
src/libcore/ops/arith.rs:#[lang = "add"]
src/libcore/ops/arith.rs:#[lang = "sub"]
src/libcore/ops/arith.rs:#[lang = "mul"]
src/libcore/ops/arith.rs:#[lang = "div"]
src/libcore/ops/arith.rs:#[lang = "rem"]
src/libcore/ops/arith.rs:#[lang = "neg"]
src/libcore/ops/arith.rs:#[lang = "add_assign"]
src/libcore/ops/arith.rs:#[lang = "sub_assign"]
src/libcore/ops/arith.rs:#[lang = "mul_assign"]
src/libcore/ops/arith.rs:#[lang = "div_assign"]
src/libcore/ops/arith.rs:#[lang = "rem_assign"]
src/libcore/cmp.rs:#[lang = "eq"]
src/libcore/cmp.rs:#[lang = "ord"]
src/libcore/ptr.rs:#[lang = "drop_in_place"]
src/libcore/ptr.rs:#[lang = "const_ptr"]
src/libcore/ptr.rs:#[lang = "mut_ptr"]
src/libcore/panicking.rs:#[lang = "panic"]
src/libcore/panicking.rs:#[lang = "panic_bounds_check"]
src/libcore/panicking.rs:#[lang = "panic_fmt"]
src/libcore/clone.rs:#[lang = "clone"]
src/libcore/marker.rs:#[lang = "send"]
src/libcore/marker.rs:#[lang = "sized"]
src/libcore/marker.rs:#[lang = "unsize"]
src/libcore/marker.rs:#[lang = "copy"]
src/libcore/marker.rs:#[lang = "sync"]
src/libcore/marker.rs:#[lang = "phantom_data"]
src/libcore/marker.rs:#[lang = "freeze"]
src/libcore/cell.rs:#[lang = "unsafe_cell"]
src/libcore/num/mod.rs:#[lang = "i8"]
src/libcore/num/mod.rs:#[lang = "i16"]
src/libcore/num/mod.rs:#[lang = "i32"]
src/libcore/num/mod.rs:#[lang = "i64"]
src/libcore/num/mod.rs:#[lang = "i128"]
src/libcore/num/mod.rs:#[lang = "isize"]
src/libcore/num/mod.rs:#[lang = "isize"]
src/libcore/num/mod.rs:#[lang = "isize"]
src/libcore/num/mod.rs:#[lang = "u8"]
src/libcore/num/mod.rs:#[lang = "u16"]
src/libcore/num/mod.rs:#[lang = "u32"]
src/libcore/num/mod.rs:#[lang = "u64"]
src/libcore/num/mod.rs:#[lang = "u128"]
src/libcore/num/mod.rs:#[lang = "usize"]
src/libcore/num/mod.rs:#[lang = "usize"]
src/libcore/num/mod.rs:#[lang = "usize"]
src/libcore/fmt/mod.rs:#[lang = "debug_trait"]
src/libcore/nonzero.rs:#[lang = "non_zero"]
```</details>

Note that `eh_personality` and `eh_unwind_resume` are defined multiple times because it's platform specific.

[QuietMisdreavus]

IMO this is more fit for the Unstable Book, in the chapter for lang_items.

[Havvy]

Fixing in the Unstable Book via rust-lang/rust#45181