To support CI job on riscv64 self hosted runner

.github/workflows/main.yaml

@@ -42,6 +42,9 @@ jobs:
   test:
     name: Build and test
     timeout-minutes: 60
+    # NOTE: self-hosted riscv64 runners are experimental and may be flaky.
+    # Do not block CI on failures from this platform for now.
+    continue-on-error: ${{ matrix.os == 'self-hosted-riscv64' }}
     strategy:
       fail-fast: false
       matrix:
@@ -72,6 +75,8 @@ jobs:
           os: ubuntu-24.04
         - target: powerpc64le-unknown-linux-gnu
           os: ubuntu-24.04-ppc64le
+        - target: riscv64gc-unknown-linux-gnu
+          os: self-hosted-riscv64
         - target: riscv64gc-unknown-linux-gnu
           os: ubuntu-24.04
         - target: s390x-unknown-linux-gnu
@@ -100,7 +105,9 @@ jobs:
         - target: x86_64-pc-windows-gnu
           os: windows-2025
           channel: nightly-x86_64-gnu
-    runs-on: ${{ matrix.os }}
+    runs-on: ${{ matrix.os ||
+               matrix.os == 'self-hosted-riscv64' && fromJSON('["self-hosted","linux","riscv64"]')
+              }}
     needs: [calculate_vars]
     env:
       BUILD_ONLY: ${{ matrix.build_only }}
@@ -133,8 +140,10 @@ jobs:
         rustup target add "${{ matrix.target }}"
 
     - uses: taiki-e/install-action@nextest
+      if: matrix.os != 'self-hosted-riscv64'
 
     - uses: Swatinem/rust-cache@v2
+      if: matrix.os != 'self-hosted-riscv64'
       with:
         key: ${{ matrix.target }}
     - name: Cache Docker layers
@@ -148,8 +157,18 @@ jobs:
     - uses: docker/setup-buildx-action@v3
       if: matrix.os == 'ubuntu-24.04'
 
+    - name: Prepare mirrored sources (self-hosted riscv64)
+      if: matrix.os == 'self-hosted-riscv64'
+      run: |
+        sed -i 's|https://github.com|https://community-ci.openruyi.cn|g' ./ci/download-compiler-rt.sh
+        sed -i 's|llvm-project-rustc-${rust_llvm_version}|llvm-project|g' ./ci/download-compiler-rt.sh
+        sed -i 's|https://github.com/kraj/musl.git|https://community-ci.openruyi.cn/others/kraj-musl.git|g' ./ci/update-musl.sh
+        sed -i 's|https://github.com/japaric/utest|https://community-ci.openruyi.cn/others/japaric-utest|g' ./builtins-test/Cargo.toml
+      shell: bash
+
     - name: Cache compiler-rt
       id: cache-compiler-rt
+      if: matrix.os != 'self-hosted-riscv64'
       uses: actions/cache@v4
       with:
         path: compiler-rt
@@ -166,7 +185,7 @@ jobs:
       shell: bash
 
     - name: Verify API list
-      if: matrix.os == 'ubuntu-24.04'
+      if: matrix.os == 'ubuntu-24.04' || matrix.os == 'self-hosted-riscv64'
       run: python3 etc/update-api-list.py --check
 
     # Non-linux tests just use our raw script