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 #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]

Codecov Report

All modified and coverable lines are covered by tests ✅

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

❗ 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              

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[briansmith]

I see that this target is quite difficult to support. I read "If you need riscv32-linux, then yes you will need to build it." from riscv-collab/riscv-gnu-toolchain#808.

It seems like my niave and underinformed guess that riscv32gc-unknown-linux-gnu would be the easiest riscv32 target to support was wrong.

Is riscv32gc-unknown-linux-gnu the actual target you are trying to support, or were you just trying to follow my suggestion? If you don't need riscv32gc-unknown-linux-gnu but instead need a different target, I think we should focus on the one that's actually useful.

[blue-freedom-technologies]

Thank you for taking the time for this analysis.

Ok, don't forget you ask for it not me.... don't kill the messenger.

Now the bad news:
our target riscv32imac-esp-espidf is a Tier 3. Meaning target is supported but not built, distributed, or guaranteed to work.

So, for our target to work we need to have the ESP-IDF Toolchain and then have a config.toml similar to this :

[build]
target = "riscv32imac-esp-espidf"

[target.riscv32imac-esp-espidf]
linker = "/tools/riscv32-esp-elf/esp-12.2.0_20230208/riscv32-esp-elf/riscv32-esp-elf/bin/ld"

[unstable]
build-std = ["std", "panic_abort"]

[env]
MCU="esp32c6"
ESP_IDF_VERSION = "v5.1.1"
TARGET_CC = "/tools/riscv32-esp-elf/esp-12.2.0_20230208/riscv32-esp-elf/bin/riscv32-esp-elf-cc"

For the ring crate build.

As example let's run the test case ed25519_tests:

cargo build --test ed25519_tests

Result...

So ☹️, I am open to suggestions on your side....when you have the time of course.

[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,