YJIT: Relax minimum Rust version requirement to 1.58.1

We want to make it convenient for people to build YJIT and Rust version 1.58.1
or above is available on Ubuntu Jammy, Debian testing, and Fedora 36 through
the usual package manager on those systems. This saves the need to install
`rustup` for some people.

Our code is already 1.58.1 compatible so this commit simply tweaks CI to make
sure that we keep supporting that version. We still test against the latest Rust
version in `--enable-yjit=dev` builds through the Rust version available in
GitHub's CI image.

Rust versions older than 1.58.1 might build YJIT today, but we might make
incompatible changes in the future.

Co-authored-by: Maxime Chevalier-Boisvert <maxime.chevalierboisvert@shopify.com>

.github/workflows/yjit-ubuntu.yml

@@ -42,7 +42,8 @@ jobs:
             configure: "--with-gcc=clang-12 --enable-yjit=dev"
 
           - test_task: "check"
-            configure: "--enable-yjit" # release build
+            configure: "--enable-yjit RUSTC='rustc +1.58.1'" # release build
+            rust_version: "1.58.1"
 
           - test_task: "check"
             configure: "--enable-yjit=dev"
@@ -70,6 +71,9 @@ jobs:
           set -x
           sudo apt-get update -q || :
           sudo apt-get install --no-install-recommends -q -y build-essential libssl-dev libyaml-dev libreadline6-dev zlib1g-dev libncurses5-dev libffi-dev bison autoconf ruby
+      - name: Install Rust
+        if: ${{ matrix.rust_version }}
+        run: rustup install ${{ matrix.rust_version }} --profile minimal
       - name: git config
         run: |
           git config --global advice.detachedHead 0

yjit/Cargo.toml

@@ -6,7 +6,7 @@
 name = "yjit"
 version = "0.1.0"       # YJIT version
 edition = "2021"        # Rust 2021 edition to compile with
-rust-version = "1.60.0" # Minimally supported rust version
+rust-version = "1.58.1" # Minimally supported rust version
 publish = false         # Don't publish to crates.io
 
 [lib]