Replace the musl submodule with a download script

The submodule was causing issues in rust-lang/rust, so eliminiate it
here. `build-musl` is also removed from `libm-test`'s default features
so the crate doesn't need to be built by default.

library/compiler-builtins/.github/workflows/main.yaml

@@ -108,8 +108,6 @@ jobs:
     - name: Print runner information
       run: uname -a
     - uses: actions/checkout@v4
-      with:
-        submodules: true
     - name: Install Rust (rustup)
       shell: bash
       run: |
@@ -146,6 +144,10 @@ jobs:
       shell: bash
     - run: echo "RUST_COMPILER_RT_ROOT=$(realpath ./compiler-rt)" >> "$GITHUB_ENV"
       shell: bash
+      
+    - name: Download musl source
+      run: ./ci/update-musl.sh
+      shell: bash
 
     - name: Verify API list
       if: matrix.os == 'ubuntu-24.04'
@@ -182,8 +184,6 @@ jobs:
     timeout-minutes: 10
     steps:
     - uses: actions/checkout@v4
-      with:
-        submodules: true
     # Unlike rustfmt, stable clippy does not work on code with nightly features.
     - name: Install nightly `clippy`
       run: |
@@ -191,6 +191,8 @@ jobs:
         rustup default nightly
         rustup component add clippy
     - uses: Swatinem/rust-cache@v2
+    - name: Download musl source
+      run: ./ci/update-musl.sh
     - run: cargo clippy --workspace --all-targets
 
   benchmarks:
@@ -205,8 +207,6 @@ jobs:
     runs-on: ${{ matrix.os }}
     steps:
     - uses: actions/checkout@master
-      with:
-        submodules: true
     - uses: taiki-e/install-action@cargo-binstall
 
     - name: Set up dependencies
@@ -223,6 +223,8 @@ jobs:
     - uses: Swatinem/rust-cache@v2
       with:
         key: ${{ matrix.target }}
+    - name: Download musl source
+      run: ./ci/update-musl.sh
 
     - name: Run icount benchmarks
       env:
@@ -256,8 +258,6 @@ jobs:
     timeout-minutes: 10
     steps:
     - uses: actions/checkout@v4
-      with:
-        submodules: true
     - name: Install Rust (rustup)
       run: rustup update nightly --no-self-update && rustup default nightly
       shell: bash
@@ -292,8 +292,6 @@ jobs:
     timeout-minutes: 10
     steps:
     - uses: actions/checkout@v4
-      with:
-        submodules: true
     - name: Install stable `rustfmt`
       run: rustup set profile minimal && rustup default stable && rustup component add rustfmt
     - run: cargo fmt -- --check
@@ -317,13 +315,13 @@ jobs:
       TO_TEST: ${{ matrix.to_test }}
     steps:
       - uses: actions/checkout@v4
-        with:
-          submodules: true
       - name: Install Rust
         run: |
           rustup update nightly --no-self-update
           rustup default nightly
       - uses: Swatinem/rust-cache@v2
+      - name: download musl source
+        run: ./ci/update-musl.sh
       - name: Run extensive tests
         run: ./ci/run-extensive.sh
       - name: Print test logs if available

library/compiler-builtins/.gitignore

@@ -14,3 +14,6 @@ iai-home
 *.bk
 *.rs.bk
 .#*
+
+# Manually managed
+crates/musl-math-sys/musl

library/compiler-builtins/.gitmodules

@@ -1,4 +0,0 @@
-[submodule "crates/musl-math-sys/musl"]
-	path = crates/musl-math-sys/musl
-	url = https://git.musl-libc.org/git/musl
-	shallow = true

library/compiler-builtins/ci/update-musl.sh

@@ -0,0 +1,15 @@
+#!/bin/sh
+# Download musl to a repository for `musl-math-sys`
+
+set -eux
+
+url=git://git.musl-libc.org/musl
+ref=c47ad25ea3b484e10326f933e927c0bc8cded3da
+dst=crates/musl-math-sys/musl
+
+if ! [ -d "$dst" ]; then
+    git clone "$url" "$dst" --single-branch --depth=1000
+fi
+
+git -C "$dst" fetch "$url" --depth=1
+git -C "$dst" checkout "$ref"

library/compiler-builtins/crates/musl-math-sys/build.rs

@@ -120,7 +120,7 @@ fn build_musl_math(cfg: &Config) {
     let arch_dir = musl_dir.join("arch").join(&cfg.musl_arch);
     assert!(
         math.exists(),
-        "musl source not found. Is the submodule up to date?"
+        "musl source not found. You may need to run `./ci/update-musl.sh`."
     );
 
     let source_map = find_math_source(&math, cfg);

library/compiler-builtins/libm-test/Cargo.toml

@@ -6,7 +6,7 @@ publish = false
 license = "MIT OR Apache-2.0"
 
 [features]
-default = ["build-mpfr", "build-musl", "unstable-float"]
+default = ["build-mpfr", "unstable-float"]
 
 # Propagated from libm because this affects which functions we test.
 unstable-float = ["libm/unstable-float", "rug?/nightly-float"]