Set the MSRV to 1.63 and document it as such

Fixes: https://github.com/rust-lang/libm/issues/330

library/compiler-builtins/libm/.github/workflows/main.yml

@@ -35,13 +35,17 @@ jobs:
     - run: cargo generate-lockfile
     - run: ./ci/run-docker.sh ${{ matrix.target }}
 
-  stable:
-    name: Build succeeds on stable
+  msrv:
+    name: Check MSRV
     runs-on: ubuntu-latest
     steps:
     - uses: actions/checkout@master
+    - run: |
+        msrv="$(perl -ne 'print if s/rust-version\s*=\s*"(.*)"/\1/g' Cargo.toml)"
+        echo "MSRV: $msrv"
+        echo "MSRV=$msrv" >> "$GITHUB_ENV"
     - name: Install Rust
-      run: rustup update stable && rustup default stable
+      run: rustup update "$MSRV" && rustup default "$MSRV"
     - run: cargo build -p libm
 
 

library/compiler-builtins/libm/Cargo.toml

@@ -11,6 +11,7 @@ repository = "https://github.com/rust-lang/libm"
 version = "0.2.9"
 edition = "2021"
 exclude = ["/ci/", "/.github/workflows/"]
+rust-version = "1.63"
 
 [features]
 default = []

library/compiler-builtins/libm/README.md

@@ -34,6 +34,10 @@ To run all benchmarks:
 
 Please check [CONTRIBUTING.md](CONTRIBUTING.md)
 
+## Minimum Rust version policy
+
+This crate supports rustc 1.63 and newer.
+
 ## License
 
 Usage is licensed under the MIT license ([LICENSE-MIT](LICENSE-MIT) or