meson: Fix detection of glib-mkenums under MSYS2

Under MSYS2 glib-mkenums is an executable and has a .exe extension and
the path does not end with "glib-mkenums".

Make the script compare the path without the file extension instead.

https://bugzilla.gnome.org/show_bug.cgi?id=796273

libs/gst/controller/controller_mkenum.py

@@ -37,7 +37,7 @@ argn = 1
 for arg in sys.argv[1:]:
     cmd.append(arg)
     argn += 1
-    if arg.endswith('glib-mkenums'):
+    if os.path.splitext(arg)[0].endswith('glib-mkenums'):
         break
 ofilename = sys.argv[argn]
 headers = sys.argv[argn + 1:]