CI: add an Alpine Edge build on Sourcehut

.builds/alpine.yml

@@ -0,0 +1,28 @@
+image: alpine/edge
+packages:
+  - eudev-dev
+  - mesa-dev
+  - meson
+  - libinput-dev
+  - libxkbcommon-dev
+  - pixman-dev
+  - wayland-dev
+  - wayland-protocols
+  - xorg-server-xwayland
+sources:
+  - https://github.com/swaywm/wlroots
+  - https://github.com/Hjdskes/cage
+tasks:
+  # Install wlroots, which is required by Cage. Note that we compile a tagged
+  # version, instead of master, to avoid any breaking changes in wlroots.
+  - wlroots: |
+      cd wlroots
+      # This corresponds to the tag of 0.5.0
+      git checkout c9137cba691b57c3eaf3ff94f9bf8e623f66ccc5
+      meson --prefix=/usr build -Drootston=false -Dexamples=false
+      ninja -C build
+      sudo ninja -C build install
+  - build: |
+      cd cage
+      meson build -Dxwayland=true
+      ninja -C build