[gdk-pixbuf] (9 commits) ...Merge branch 'macos-ci' into 'master'

[Emmanuele Bassi <ebassi src gnome org>]

Summary of changes:

  9832e8f... ci: Add a macos build (*)
  edcb921... Try to fix libffi build (*)
  b003b93... Don't build docs or installed tests on MacOS (*)
  9326d96... Skip resource tests with glib subproject (*)
  c1c91ac... Deal with glib-compile-resources not in the PATH (*)
  2839b5c... Pass glib-compile-resources's path to gen-resources.py (*)
  7edbb02... Minimise bandwidth use for subprojects (*)
  048938a... ci: Limit macOS builds (*)
  7ccbdf5... Merge branch 'macos-ci' into 'master'

(*) This commit already existed in another branch; no separate mail sent