Move the stdout flush to the windows file, since it's only needed there

cibuildwheel/__main__.py

@@ -136,7 +136,6 @@ def print_preamble(platform, build_options):
         print('  %s: %r' % (option, value))
 
     print('\nHere we go!\n')
-    sys.stdout.flush()
 
 if __name__ == '__main__':
     main()

cibuildwheel/windows.py

@@ -12,6 +12,7 @@ from .util import prepare_command
 
 def build(project_dir, package_name, output_dir, test_command, test_requires, before_build, skip):
     # Python under AppVeyor/Windows seems to be buffering by default, giving problems interleaving subprocess call output with unflushed calls to 'print'
+    sys.stdout.flush()
     sys.stdout = os.fdopen(sys.stdout.fileno(), 'w', 0)
 
     # run_with_env is a cmd file that sets the right environment variables to