impl TryFrom from native to NonZero

[heca-project]

You can now do the following:

```
let p: u8 = 5;
let q: NonZeroU8 = p.try_into()?;
```

[rust-highfive]

Thanks for the pull request, and welcome! The Rust team is excited to review your changes, and you should hear from @kennytm (or someone else) soon.

If any changes to this PR are deemed necessary, please add them as extra commits. This ensures that the reviewer can see what has changed since they last reviewed the code. Due to the way GitHub handles out-of-date commits, this should also make it reasonably obvious what issues have or haven't been addressed. Large or tricky changes may require several passes of review and changes.

Please see the contribution instructions for more information.

[rust-highfive]

The job mingw-check of your PR failed (pretty log, raw log). Through arcane magic we have determined that the following fragments from the build log may contain information about the problem.

Click to expand the log.

##[section]Starting: Linux mingw-check
##[section]Starting: Initialize job
Agent name: 'Hosted Agent'
Agent machine name: 'fv-az578'
Current agent version: '2.169.1'
##[group]Operating System
16.04.6
LTS
LTS
##[endgroup]
##[group]Virtual Environment
Environment: ubuntu-16.04
Version: 20200517.1
Included Software: https://github.com/actions/virtual-environments/blob/ubuntu16/20200517.1/images/linux/Ubuntu1604-README.md
##[endgroup]
Agent running as: 'vsts'
Prepare build directory.
Set build variables.
Download all required tasks.
Download all required tasks.
Downloading task: Bash (3.163.2)
Checking job knob settings.
   Knob: AgentToolsDirectory = /opt/hostedtoolcache Source: ${AGENT_TOOLSDIRECTORY} 
   Knob: AgentPerflog = /home/vsts/perflog Source: ${VSTS_AGENT_PERFLOG} 
Start tracking orphan processes.
##[section]Finishing: Initialize job
##[section]Starting: Configure Job Name
==============================================================================
---
========================== Starting Command Output ===========================
[command]/bin/bash --noprofile --norc /home/vsts/work/_temp/132a7419-1ceb-4bf1-82f3-1a3c87bf7087.sh

##[section]Finishing: Disable git automatic line ending conversion
##[section]Starting: Checkout rust-lang/rust@refs/pull/72846/merge to s
Task         : Get sources
Description  : Get sources from a repository. Supports Git, TfsVC, and SVN repositories.
Version      : 1.0.0
Author       : Microsoft
---
##[command]git remote add origin https://github.com/rust-lang/rust
##[command]git config gc.auto 0
##[command]git config --get-all http.https://github.com/rust-lang/rust.extraheader
##[command]git config --get-all http.proxy
##[command]git -c http.extraheader="AUTHORIZATION: basic ***" fetch --force --tags --prune --progress --no-recurse-submodules --depth=2 origin +refs/heads/*:refs/remotes/origin/* +refs/pull/72846/merge:refs/remotes/pull/72846/merge
---
 ---> 3adb0605cc65
Step 6/7 : ENV RUN_CHECK_WITH_PARALLEL_QUERIES 1
 ---> Using cache
 ---> 28dbc326cb7f
Step 7/7 : ENV SCRIPT python3 ../x.py test src/tools/expand-yaml-anchors &&            python3 ../x.py check --target=i686-pc-windows-gnu --host=i686-pc-windows-gnu &&            python3 ../x.py build --stage 0 src/tools/build-manifest &&            python3 ../x.py test --stage 0 src/tools/compiletest &&            python3 ../x.py test src/tools/tidy &&            python3 ../x.py doc --stage 0 src/libstd &&            /scripts/validate-toolstate.sh
 ---> 537a01811900
Successfully built 537a01811900
Successfully tagged rust-ci:latest
Built container sha256:537a018119009dc218456238dec90b5530050db1e2a1e166550c218003f6159d
---
    Checking rustc_feature v0.0.0 (/checkout/src/librustc_feature)
    Checking fmt_macros v0.0.0 (/checkout/src/libfmt_macros)
    Checking rustc_ast_pretty v0.0.0 (/checkout/src/librustc_ast_pretty)
    Checking rustc_hir v0.0.0 (/checkout/src/librustc_hir)
    Checking rustc_query_system v0.0.0 (/checkout/src/librustc_query_system)
    Checking chalk-rust-ir v0.10.0
    Checking rustc_parse v0.0.0 (/checkout/src/librustc_parse)
    Checking rustc_hir_pretty v0.0.0 (/checkout/src/librustc_hir_pretty)
    Checking rustc_ast_lowering v0.0.0 (/checkout/src/librustc_ast_lowering)
---
configure: build.locked-deps    := True
configure: rust.codegen-units-std := 1
configure: rust.verify-llvm-ir  := True
configure: rust.channel         := nightly
configure: build.configure-args := ['--enable-sccache', '--disable-manage-submodu ...
configure: writing `config.toml` in current directory
configure: 
configure: run `python /checkout/x.py --help`
configure: 
---
Hugepagesize:       2048 kB
DirectMap4k:      135104 kB
DirectMap2M:     4059136 kB
DirectMap1G:     5242880 kB
+ python3 ../x.py test src/tools/expand-yaml-anchors
Ensuring the YAML anchors in the GitHub Actions config were expanded
Ensuring the YAML anchors in the GitHub Actions config were expanded
Building stage0 tool expand-yaml-anchors (x86_64-unknown-linux-gnu)
   Compiling unicode-xid v0.2.0
   Compiling syn v1.0.11
   Compiling linked-hash-map v0.5.2
   Compiling lazy_static v1.4.0
   Compiling lazy_static v1.4.0
   Compiling yaml-rust v0.4.3
   Compiling quote v1.0.2
   Compiling thiserror-impl v1.0.5
   Compiling thiserror v1.0.5
   Compiling yaml-merge-keys v0.4.0
   Compiling expand-yaml-anchors v0.1.0 (/checkout/src/tools/expand-yaml-anchors)
Build completed successfully in 0:00:30
+ python3 ../x.py check --target=i686-pc-windows-gnu --host=i686-pc-windows-gnu
    Finished dev [unoptimized] target(s) in 0.23s
Checking rustdoc artifacts (x86_64-unknown-linux-gnu -> i686-pc-windows-gnu)
---
    Checking rustc_feature v0.0.0 (/checkout/src/librustc_feature)
    Checking fmt_macros v0.0.0 (/checkout/src/libfmt_macros)
    Checking rustc_ast_pretty v0.0.0 (/checkout/src/librustc_ast_pretty)
    Checking rustc_hir v0.0.0 (/checkout/src/librustc_hir)
    Checking rustc_query_system v0.0.0 (/checkout/src/librustc_query_system)
    Checking chalk-rust-ir v0.10.0
    Checking rustc_parse v0.0.0 (/checkout/src/librustc_parse)
    Checking rustc_hir_pretty v0.0.0 (/checkout/src/librustc_hir_pretty)
    Checking rustc_ast_lowering v0.0.0 (/checkout/src/librustc_ast_lowering)
---
Found 0 error codes with no tests
Done!


command did not execute successfully: "/checkout/obj/build/x86_64-unknown-linux-gnu/stage0-tools-bin/tidy" "/checkout/src" "/checkout/obj/build/x86_64-unknown-linux-gnu/stage0/bin/cargo"


some tidy checks failed
failed to run: /checkout/obj/build/bootstrap/debug/bootstrap test src/tools/tidy
failed to run: /checkout/obj/build/bootstrap/debug/bootstrap test src/tools/tidy
Build completed unsuccessfully in 0:00:35
== clock drift check ==
  local time: Mon Jun  1 03:33:10 UTC 2020
  network time: Mon, 01 Jun 2020 03:33:10 GMT
== end clock drift check ==

##[error]Bash exited with code '1'.
##[section]Finishing: Run build
##[section]Starting: Checkout rust-lang/rust@refs/pull/72846/merge to s
Task         : Get sources
Description  : Get sources from a repository. Supports Git, TfsVC, and SVN repositories.
Version      : 1.0.0
Author       : Microsoft
Author       : Microsoft
Help         : [More Information](https://go.microsoft.com/fwlink/?LinkId=798199)
==============================================================================
Cleaning any cached credential from repository: rust-lang/rust (GitHub)
##[section]Finishing: Checkout rust-lang/rust@refs/pull/72846/merge to s
Cleaning up task key
Start cleaning up orphan processes.
Terminate orphan process: pid (4130) (python)
##[section]Finishing: Finalize Job

I'm a bot! I can only do what humans tell me to, so if this was not helpful or you have suggestions for improvements, please ping or otherwise contact @rust-lang/infra. (Feature Requests)

[kennytm]

still a

tidy error: /checkout/src/libcore/num/mod.rs:114: trailing whitespace

---

r? @SimonSapin

[poliorcetics]

In #72717 I had tests written for this if you want them. Writing a doc_comment!(...) like the one a few lines above might nice too.

[dtolnay]

I'll close this in favor of #72717 which was opened first and has the same impls along with tests.

Thanks anyway!