Add riscv32 support

[blue-freedom-technologies]

I am happy to accept a PR that adds riscv32 support. I suggest we start with riscv32gc-unknown-linux-gnu since we can just copy-paste-edit the changes from PR https://github.com/briansmith/ring/pull/1627, at least for for target.h, mk/cargo.sh, mk/install-build-tools.sh.

[blue-freedom-technologies]

Hi @briansmith,

There are two points here that we need your advise: -OPENSSL_32_BIT -newliblinux-multilib

Thank you for your time.

Cheers,

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Comparison is base (7f8fb38) 96.03% compared to head (49c9f56) 96.02%. Report is 1 commits behind head on main.

:exclamation: Current head 49c9f56 differs from pull request most recent head 41d6076. Consider uploading reports for the commit 41d6076 to get more accurate results

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1880      +/-   ##
==========================================
- Coverage   96.03%   96.02%   -0.02%     
==========================================
  Files         136      136              
  Lines       20761    20776      +15     
  Branches      226      226              
==========================================
+ Hits        19938    19950      +12     
- Misses        789      792       +3     
  Partials       34       34              

:umbrella: View full report in Codecov by Sentry.
:loudspeaker: Have feedback on the report? Share it here.

[blue-freedom-technologies]

On a more happy note I have added the target_os = "espidf".

Thank you for your time addressing all of these troubles.

Cheers,