appveyor: skip two redundant builds to speed up CI on Windows

Skip the Appveyor 32-bit Windows Server 2016 job, and 64-bit Windows
Server 2012 R2 job. The remaining 2 jobs still provide coverage of
64/32-bit, and Windows Server 2016/2012 R2.

Also set fast_finish, so failed jobs terminate the build immediately.

Fixes bug 29601; bugfix on 0.3.5.4-alpha.

.appveyor.yml

@@ -25,6 +25,25 @@ environment:
     # hardening doesn't work with mingw-w64-x86_64-gcc, because it's gcc 8
     hardening: --disable-gcc-hardening
 
+matrix:
+  # Don't keep building failing jobs
+  fast_finish: true
+  # Skip the 32-bit Windows Server 2016 job, and the 64-bit Windows Server
+  # 2012 R2 job, to speed up the build.
+  # The environment variables must be listed without the 'environment' tag.
+  exclude:
+    - image: Visual Studio 2017
+      target: i686-w64-mingw32
+      compiler_path: mingw32
+      mingw_prefix: mingw-w64-i686
+      hardening:
+    - image: Visual Studio 2015
+      target: x86_64-w64-mingw32
+      compiler_path: mingw64
+      mingw_prefix: mingw-w64-x86_64
+      # hardening doesn't work with mingw-w64-x86_64-gcc, because it's gcc 8
+      hardening: --disable-gcc-hardening
+
 install:
 - ps: >-
     Function Execute-Command ($commandPath)

changes/bug29601

@@ -0,0 +1,6 @@
+  o Minor bugfixes (Windows, CI):
+    - Skip the Appveyor 32-bit Windows Server 2016 job, and 64-bit Windows
+      Server 2012 R2 job. The remaining 2 jobs still provide coverage of
+      64/32-bit, and Windows Server 2016/2012 R2. Also set fast_finish, so
+      failed jobs terminate the build immediately.
+      Fixes bug 29601; bugfix on 0.3.5.4-alpha.