Fix build on Windows arm64

[wezm]

Building on a Windows Arm machine results in this error:

error[E0381]: used binding `display_ptr` isn't initialized
   --> src\native\windows.rs:279:8
    |
267 |     let display_ptr: isize;
    |         ----------- binding declared here but left uninitialized
...
279 |     if display_ptr == 0 {
    |        ^^^^^^^^^^^ `display_ptr` used here but it isn't initialized
    |
help: consider assigning a value
    |
267 |     let display_ptr: isize = 42;
    |                            ++++

Since the code seems to be using target_arch to conditionally compile based on 32/64-bit arch I changed it to use target_pointer_width instead. After this change I can run the examples:

[not-fl3]

Thanks for PR!