build: Fix type signature of rich comparison dunders

There are three problems:

1) Dunders like `__lt__` and `__gt__` don't return bool, they return
   either a bool or the NotImplemented singleton to signal that they don't
   know how to be compared.
2) The don't take type object, the take `typing.Any`
3) They need to return NotImplemented if the comparison is not
   implemented, this allows python to try the inverse dunder from the
   other object. If that object returns NotImplemented as well a
   TypeError is raised.

mesonbuild/build.py

@@ -355,16 +355,24 @@ a hard error in the future.''' % name)
         if not hasattr(self, 'typename'):
             raise RuntimeError('Target type is not set for target class "{}". This is a bug'.format(type(self).__name__))
 
-    def __lt__(self, other: object) -> bool:
+    def __lt__(self, other: typing.Any) -> typing.Union[bool, 'NotImplemented']:
+        if not hasattr(other, 'get_id') and not callable(other.get_id):
+            return NotImplemented
         return self.get_id() < other.get_id()
 
-    def __le__(self, other: object) -> bool:
+    def __le__(self, other: typing.Any) -> typing.Union[bool, 'NotImplemented']:
+        if not hasattr(other, 'get_id') and not callable(other.get_id):
+            return NotImplemented
         return self.get_id() <= other.get_id()
 
-    def __gt__(self, other: object) -> bool:
+    def __gt__(self, other: typing.Any) -> typing.Union[bool, 'NotImplemented']:
+        if not hasattr(other, 'get_id') and not callable(other.get_id):
+            return NotImplemented
         return self.get_id() > other.get_id()
 
-    def __ge__(self, other: object) -> bool:
+    def __ge__(self, other: typing.Any) -> typing.Union[bool, 'NotImplemented']:
+        if not hasattr(other, 'get_id') and not callable(other.get_id):
+            return NotImplemented
         return self.get_id() >= other.get_id()
 
     def get_install_dir(self, environment):