try to fix alpine from scratch.

.github/workflows/alpine.yml

@@ -0,0 +1,63 @@
+name: Alpine Linux
+
+on:
+  push:
+  pull_request:
+
+jobs:
+  build:
+    name: Build on Alpine ${{ matrix.arch }}
+
+    runs-on: ubuntu-latest
+
+    strategy:
+      fail-fast: false
+      matrix:
+        arch:
+          - x86_64
+          - x86
+          - aarch64
+          - armv7
+          - ppc64le
+          - riscv64
+
+    steps:
+      - name: Checkout repository
+        uses: actions/checkout@v7
+
+      - name: Install Alpine Linux for ${{ matrix.arch }}
+        uses: jirutka/setup-alpine@v1
+        with:
+          arch: ${{ matrix.arch }}
+
+          # Keep CI reproducible.
+          # riscv64 currently uses edge because stable Alpine support
+          # for this architecture can lag behind the other architectures.
+          branch: ${{ matrix.arch == 'riscv64' && 'edge' || 'v3.23' }}
+
+          packages: >
+            build-base
+            cmake
+            linux-headers
+            git
+            bash
+
+      - name: Prepare
+        run: |
+          cmake \
+            -DFASTFLOAT_TEST=ON \
+            -B build
+        shell: alpine.sh {0}
+
+      - name: Build
+        run: |
+          cmake --build build
+        shell: alpine.sh {0}
+
+      - name: Test
+        run: |
+          ctest \
+            --test-dir build \
+            -R basictest \
+            --output-on-failure
+        shell: alpine.sh {0}