ci/appveyor: use -A option with all MSVC versions (#1513)

To simplify the initialization. The ` Win64` method was meant for old
CMake versions not in use in CI.

Also pass the `-A` option without a space to make PowerShell pass
the option as expected by CMake.

appveyor.yml

@@ -143,18 +143,10 @@ build_script:
   - ps: |
       $options = @('-DENABLE_WERROR=ON')
 
-      if($env:GENERATOR -eq 'Visual Studio 17 2022') {
-        if($env:PLATFORM -eq 'x86') {
-          $options += '-A Win32'
-        }
-        else {
-          $options += "-A $env:PLATFORM"
-        }
-      }
-      elseif($env:PLATFORM -eq 'x64') {
-        $env:GENERATOR += ' Win64'
-      }
       $options += "-G$env:GENERATOR"
+      if($env:PLATFORM -ne 'x86') {
+        $options += "-A$env:PLATFORM"
+      }
 
       $options += "-DCRYPTO_BACKEND=$env:CRYPTO_BACKEND"
       if($env:OPENSSL_ROOT_DIR -ne '') {