python/meson: set exe_wrapper=wine for Windows builds

Allows running the unit tests on Linux.

python/build/meson.py

@@ -1,4 +1,5 @@
 import os.path, subprocess, sys
+import platform
 
 from build.project import Project
 
@@ -43,9 +44,12 @@ strip = '{toolchain.strip}'
 pkgconfig = '{toolchain.pkg_config}'
 """)
 
-        if toolchain.is_windows:
+        if toolchain.is_windows and platform.system() != 'Windows':
             f.write(f"windres = '{toolchain.windres}'\n")
 
+            # Run unit tests with WINE when cross-building for Windows
+            print("exe_wrapper = 'wine'", file=f)
+
         f.write(f"""
 [properties]
 root = '{toolchain.install_prefix}'