CI: Manually build exiv2 0.27 for Windows package

Exiv2 0.28 dropped the old `std::wstring` path and breaks non-ASCII path
handling in Windows. While recent Windows supports using UTF-8 as
locale, it might cause other issue.

Before actual fix in <Exiv2/exiv2#2800> getting
merged, we stick to exiv2 0.27 branch for Windows build.

.github/workflows/win-nightly.yml

@@ -21,7 +21,7 @@ jobs:
         generator:
           - Ninja
         branch:
-          - { code: master, label: stable }
+          - { code: "${{ github.ref_name }}", label: stable }
         msystem:
           - UCRT64
     defaults:
@@ -53,7 +53,6 @@ jobs:
             nsis:p
             dbus-glib:p
             drmingw:p
-            exiv2:p
             gcc-libs:p
             gettext:p
             gmic:p
@@ -98,6 +97,33 @@ jobs:
           fetch-depth: 500
           submodules: true
           path: src
+      - name: Checkout exiv2 source
+        uses: actions/checkout@v3
+        with:
+          repository: 'Exiv2/exiv2'
+          # Exiv2 0.28.0 removes the old `std::wstring` path for Windows, and
+          # breaks non-ASCII path handling. We stick to 0.27 until fixes in
+          # <https://github.com/Exiv2/exiv2/pull/2800> get merged.
+          ref: '0.27-maintenance'
+          path: 'exiv2-src'
+          fetch-depth: 1
+      # Install manually compiled dependencies into MingW's prefix, so ansel
+      # will link against it and CPack will grab it.
+      - name: Manually build exiv2 dependency
+        run: |
+          cd exiv2-src
+          cmake -B build -G Ninja \
+          -DCMAKE_INSTALL_PREFIX=${MINGW_PREFIX} \
+          -DEXIV2_ENABLE_VIDEO=OFF \
+          -DEXIV2_ENABLE_NLS=ON \
+          -DEXIV2_ENABLE_XMP=ON \
+          -DEXIV2_ENABLE_CURL=ON \
+          -DEXIV2_ENABLE_WEBREADY=ON \
+          -DEXIV2_ENABLE_WIN_UNICODE=ON \
+          -DEXIV2_ENABLE_BMFF=ON
+          ninja -C build
+          ninja -C build install
+          cd ..
       - name: Update lensfun data
         run: |
           lensfun-update-data