[FRONTEND] In JITFunction: infer constexpr arg only if annotated as such (#1345)

Fixed `JITFunction.__init__` to mark args as constexpr only when the
annotation is actually `tl.constexpr`, rather than treating any
annotated arg as constexpr.

python/triton/runtime/jit.py

@@ -316,7 +316,9 @@ def {self.fn.__name__}({', '.join(self.arg_names)}, grid, num_warps=4, num_stage
         self.annotations = {self.arg_names.index(name): ty for name, ty in fn.__annotations__.items()}
         self.__annotations__ = fn.__annotations__
         # index of constexprs
-        self.constexprs = [self.arg_names.index(ann) for ann in self.__annotations__.keys()]
+        from triton.language.core import \
+            constexpr  # import here rather than at module level due to circular import tangle
+        self.constexprs = [index for index, ty in self.annotations.items() if issubclass(ty, constexpr)]
         # launcher
         self.run = self._make_launcher()
         # re-use docs of wrapped function