CI: Build documentation of dependencies

Build documentation of libsigc++, glibmm, cairomm, or else pangomm's
inheritance diagrams will be incomplete due to missing tag files.

.gitlab-ci.yml

@@ -55,7 +55,7 @@ build_deps:
     - git clone --branch 3.2.0 --depth 1 https://github.com/libsigcplusplus/libsigcplusplus.git libsigc
     - cd libsigc
     - mkdir _build && cd _build
-    - meson --prefix=/usr --libdir=lib -Dbuild-documentation=false -Dbuild-examples=false -Dbuildtype=release
+    - meson --prefix=/usr --libdir=lib -Dvalidation=false -Dbuild-examples=false -Dbuildtype=release
     - meson compile
     - meson install
     - cd ../..
@@ -65,7 +65,7 @@ build_deps:
     - git clone --branch 2.70.0 --depth 1 https://gitlab.gnome.org/GNOME/glibmm.git glibmm
     - cd glibmm
     - mkdir _build && cd _build
-    - meson --prefix=/usr --libdir=lib -Dbuild-documentation=false -Dbuild-examples=false -Dbuildtype=release
+    - meson --prefix=/usr --libdir=lib -Dbuild-examples=false -Dbuildtype=release
     - meson compile
     - cd ../..
     - fi
@@ -74,7 +74,7 @@ build_deps:
     - git clone --branch 1.16.1 --depth 1 https://gitlab.freedesktop.org/cairo/cairomm.git cairomm
     - cd cairomm
     - mkdir _build && cd _build
-    - meson --prefix=/usr --libdir=lib -Dbuild-documentation=false -Dbuild-examples=false -Dbuild-tests=false -Dbuildtype=release
+    - meson --prefix=/usr --libdir=lib -Dbuild-examples=false -Dbuild-tests=false -Dbuildtype=release
     - meson compile
     - cd ../..
     - fi