Bug #82645 Add CMake check for 64 bit Windows build

Description:
As of MySQL 8.0, we no longer support 32 bit Windows builds.
In fact, we already have code that won't build 32 bit.

Instead of just failing to compile, we should add a CMake check with a
helpful error message indicating that 32 bit builds are not supported.

How to repeat:
Try building 8.0 32 bit Windows. Notice that compilation fails, but CMake doesn't warn about it.

Posted by developer:
 
Noted in 8.0.1 changelog.

32-bit builds are no longer supported on Windows, but CMake failed to
detect when a 32-built build would be attempted, resulting in
compilation errors later. Now CMake detects 32-bit build attempts and
produces an appropriate error message.