Disallow some keyword arguments to gnome.mkenums.

The install argument is allowed for CustomTargets, but we use
install_header as the setting now. Also, setting a generic template when
specifying the more specific source or header template shouldn't be
allowed.

mesonbuild/modules/gnome.py

@@ -715,7 +715,7 @@ can not be used with the current version of glib-compiled-resources, due to
         known_kwargs = ['comments', 'eprod', 'fhead', 'fprod', 'ftail',
                         'identifier_prefix', 'symbol_prefix', 'template',
                         'vhead', 'vprod', 'vtail']
-        known_custom_target_kwargs = ['install', 'install_dir', 'build_always',
+        known_custom_target_kwargs = ['install_dir', 'build_always',
                                       'depends', 'depend_files']
         c_template = h_template = None
         install_header = False
@@ -724,8 +724,16 @@ can not be used with the current version of glib-compiled-resources, due to
                 sources = [value] + sources
             elif arg == 'c_template':
                 c_template = value
+                if 'template' in kwargs:
+                    raise MesonException('Mkenums does not accept both '
+                                         'c_template and template keyword '
+                                         'arguments at the same time.')
             elif arg == 'h_template':
                 h_template = value
+                if 'template' in kwargs:
+                    raise MesonException('Mkenums does not accept both '
+                                         'h_template and template keyword '
+                                         'arguments at the same time.')
             elif arg == 'install_header':
                 install_header = value
             elif arg in known_kwargs: