Cross-compile 32-bit Windows builds using 64-bit toolset

This should avoid memory limits when using 32-bit tools, which is relevant for libmongoc sources using the BSON DSL API.
If you run into memory limits when you use the 32-bit tools, try the 64-bit tools.

Author: jmikola

.github/actions/windows/prepare-build/action.yml

@@ -33,7 +33,8 @@ runs:
     - name: Enable Developer Command Prompt
       uses: ilammy/msvc-dev-cmd@v1
       with:
-        arch: ${{ inputs.arch }}
+        # Use 64-bit toolset to produce 32-bit binaries
+        arch: ${{ inputs.arch == 'x86' && 'amd64_x86' || inputs.arch }}
         toolset: ${{ steps.setup-php.outputs.toolset }}
 
     - name: phpize