AppVeyor: Switched the Qt 5.12.9 build from MinGW to MSVC

This build is only done for testing purposes, so let it build with an
alternative compiler to catch potential compilation issues early.

Zstd is not enabled for the Visual Studio build. I'm not sure how to set
that up right now, but it's not important since this build is not
distributed.

appveyor.yml

@@ -13,30 +13,32 @@ environment:
   BUTLER_API_KEY:
     secure: j7JM5L6KeqpnQukzJLsm7J6oV92SpmyEZLSoED1pZ3gQ79VIkdxtbQmTkqUNZPsz
   matrix:
-    - QTDIR: C:\Qt\5.12.9\mingw73_64
+    - QTDIR: C:\Qt\5.12.9\msvc2017_64
       PYTHONHOME: C:\Python37-x64
-      MINGW: C:\Qt\Tools\mingw730_64
-      DEFAULT_PROFILE: x86_64-w64-mingw32-gcc-7_3_0
+      DEFAULT_PROFILE: MSVC2019-x64
       PUSH_RELEASE: false
+      ENABLE_ZSTD: false
     - QTDIR: C:\Qt\5.6.3\mingw49_32
       PYTHONHOME: C:\Python37
       MINGW: C:\Qt\Tools\mingw492_32
       DEFAULT_PROFILE: i686-w64-mingw32-gcc-4_9_2
       PUSH_RELEASE: false
       PUSH_SNAPSHOT: true
+      ENABLE_ZSTD: true
       TILED_ITCH_CHANNEL: winxp-32bit
     - QTDIR: C:\Qt\5.15.0\mingw81_64
       PYTHONHOME: C:\Python37-x64
       MINGW: C:\Qt\Tools\mingw810_64
       DEFAULT_PROFILE: x86_64-w64-mingw32-gcc-8_1_0
       PUSH_RELEASE: true
       PUSH_SNAPSHOT: true
+      ENABLE_ZSTD: true
       TILED_ITCH_CHANNEL: windows-64bit
 
 matrix:
   exclude:
     - image: Visual Studio 2015
-      QTDIR: C:\Qt\5.12.9\mingw73_64
+      QTDIR: C:\Qt\5.12.9\msvc2017_64
     - image: Visual Studio 2015
       QTDIR: C:\Qt\5.15.0\mingw81_64
     - image: Visual Studio 2019
@@ -59,14 +61,11 @@ build_script:
   - if not defined APPVEYOR_PULL_REQUEST_NUMBER if [%APPVEYOR_REPO_BRANCH%]==[snapshot] if defined PUSH_SNAPSHOT set PUSH_TO_ITCH=true
   - echo Building Tiled %TILED_VERSION% (%TILED_ITCH_CHANNEL%) from %COMMITNOW%
   - git clone --depth 1 -b master https://github.com/facebook/zstd.git
-  - cd zstd/lib
-  - set CC=gcc
-  - mingw32-make -j2 libzstd.a
-  - cd ../../
+  - if defined MINGW cd zstd/lib & set CC=gcc & mingw32-make -j2 libzstd.a & cd ../../
   - qbs --version
   - qbs setup-toolchains --detect
   - qbs config defaultProfile %DEFAULT_PROFILE%
-  - qbs build --all-products config:release projects.Tiled.windowsInstaller:true projects.Tiled.enableZstd:true
+  - qbs build --all-products config:release projects.Tiled.windowsInstaller:true projects.Tiled.enableZstd:%ENABLE_ZSTD%
   - cd util\java
   - mvn --version
   - mvn clean install