Fix AppVeyor IA32 builds (#5096)

* Fix AppVeyor IA32 builds

> The default target platform name (architecture) is that of the host and is provided in the CMAKE_VS_PLATFORM_NAME_DEFAULT variable.

AppVeyor uses AMD64. Oops.

* del cmakecache

* -

* +

appveyor.yml

@@ -70,7 +70,7 @@ for:
       - job_name: Windows-x86
 
   before_build:
-  - cmake -G "Visual Studio 16 2019" ..
+  - cmake -G "Visual Studio 16 2019" -A "Win32" ..
 
 ################################
 # Windows 64-bit release build #