wayland: support vendored protocols.

mesonbuild/modules/wayland.py

@@ -112,11 +112,13 @@ def scan_xml(self, state: ModuleState, args: T.Tuple[T.List[FileOrString]], kwar
         'wayland.find_protocol',
         KwargInfo('state', str, default='stable', validator=in_set_validator({'stable', 'staging', 'unstable'})),
         KwargInfo('version', (int, NoneType)),
+        KwargInfo('vendored', bool, default=False, since='1.6.0'),
     )
     def find_protocol(self, state: ModuleState, args: T.Tuple[str], kwargs: FindProtocol) -> File:
         base_name = args[0]
         xml_state = kwargs['state']
         version = kwargs['version']
+        vendored = kwargs['vendored']
 
         if xml_state != 'stable' and version is None:
             raise MesonException(f'{xml_state} protocols require a version number.')
@@ -137,7 +139,10 @@ def find_protocol(self, state: ModuleState, args: T.Tuple[str], kwargs: FindProt
             xml_name += f'-v{version}'
         xml_name += '.xml'
 
-        path = os.path.join(self.pkgdatadir, xml_state, base_name, xml_name)
+        if vendored:
+            path = os.path.join(self.interpreter.subdir, xml_name)
+        else:
+            path = os.path.join(self.pkgdatadir, xml_state, base_name, xml_name)
 
         if not os.path.exists(path):
             raise MesonException(f'The file {path} does not exist.')