Remove AppVeyor and some Cirrus-CI components

These are replaced by GitHub actions, so we now distribute a few jobs
between GitHub Actions and Cirrus-CI which hopefully will give us a
fast turnaround.

.cirrus.yml

@@ -21,25 +21,6 @@ compile_template: &COMPILE
 # ----------
 # Linux
 
-task:
-  << : *ENVIRONMENT
-  name: linux-gcc
-  container:
-    memory: 1G
-    image: gcc:latest
-
-  # Base environment already includes the packages we need.
-
-  # One system with more excessive validation
-  compile_script:
-    - autoreconf -i
-    - ./configure CC="gcc -fsanitize=address,undefined"
-    - make -j4 CFLAGS="-g -O3 -Wall -Werror"
-
-  test_script:
-    - make check CFLAGS="-g -O3 -Wall -Werror"
-    - make distcheck
-
 task:
   << : *ENVIRONMENT
   name: linux-arm
@@ -48,8 +29,6 @@ task:
     cpu: 2
     memory: 1G
 
-  # Base environment already includes the packages we need.
-
   # NB: we could consider building a docker image with these
   # preinstalled and specifying that instead, to speed up testing.
   install_script: |
@@ -93,64 +72,6 @@ rocky_task:
 
   << : *COMPILE
 
-# ----------
-# MacOS X
-task:
-  << : *ENVIRONMENT
-  name: macosx
-  macos_instance:
-    image: ghcr.io/cirruslabs/macos-ventura-base:latest
-
-  package_install_script:
-    - brew install autoconf automake libtool
-
-  # Try building and testing a multiarch library
-  compile_script:
-    - autoreconf -i
-    - ./configure CFLAGS="-g -O3 -Wall -Werror -arch arm64 -arch x86_64"
-    - make -j4
-
-  test_script:
-    - make check
-
-# # ----------
-# # Windows MINGW.
-# # A work in progress which doesn't yet work.  It looks slow to install
-# # although *_cache can help a bit.  Maybe just stick with AppVeyor.
-# task:
-#   << : *ENVIRONMENT
-#   name: windows-1
-#   windows_container:
-#     image: cirrusci/windowsservercore:2019
-#     os_version: 2019
-# 
-#   # See https://cirrus-ci.org/guide/writing-tasks/#cache-instruction
-#   mingw_cache:
-#     # The entirety of chocholatey is heavyweight, but this is still
-#     # under half the time of installing mingw.
-#     folder: C:\Tools
-# 
-#     # default fingerprint is task name (windows-X above)
-#     populate_script:
-#       # Maybe choco install msys2 and then msys2 pacman to install
-#       # mingw, meaning we can archive the entire C:\tools dir?
-#       # - choco install -y --no-progress msys2 mingw 
-#       # - set PATH=%PATH%;\C:\tools\msys64\usr\bin
-#       # - pacman -S --noconfirm --needed automake libtool autoconf 
-# 
-#       # Msys is glacial, and installs its own broken compiler automatically
-#       # which we then replace with mingw-w64-x86_64-toolchain.
-#       # We a better way of downloading just the packages we need and running
-#       # pacman on the files directly.
-#       - choco install -y --no-progress msys2
-#       - set PATH=%PATH%;\C:\tools\msys64\usr\bin
-#       - pacman -S --noconfirm --needed base-devel mingw-w64-x86_64-toolchain mingw-w64-x86_64-zlib mingw-w64-x86_64-bzip2 mingw-w64-x86_64-xz
-# 
-#   compile_script:
-#     - c:\tools\msys64\usr\bin\bash --login "autoreconf -i"
-#     - c:\tools\msys64\usr\bin\bash "./configure"
-#     - c:\tools\msys64\usr\bin\bash "make -j4"
-
 # ----------
 # FreeBSD
 task: