windows_build_wheels: By default, run pip with --upgrade flag

Author: jcfr

scripts/windows_build_wheels.py

@@ -22,10 +22,14 @@
 from wheel_builder_utils import push_dir, push_env
 
 
-def pip_install(python_dir, package):
+def pip_install(python_dir, package, upgrade=True):
     pip = os.path.join(python_dir, "Scripts", "pip.exe")
     print("Installing %s using %s" % (package, pip))
-    check_call([pip, "install", package])
+    args = [pip, "install"]
+    if upgrade:
+        args.append("--upgrade")
+    args.append(package)
+    check_call(args)
 
 
 def prepare_build_env(python_version):