move codegen binary to the common build system (#74470)

Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/74470

Internally, use it as well.
ghstack-source-id: 152438657

Test Plan: Rely on CI to validate.

Reviewed By: malfet

Differential Revision: D35011144

fbshipit-source-id: fb7247470df579ae23fcbc74bd2f8d6cc55cf657
(cherry picked from commit d9b476e2507807097a59c0b0a5ddf029d8dc0ab3)

tools/bazel.bzl

@@ -21,6 +21,7 @@ rules = struct(
     filegroup = native.filegroup,
     glob = native.glob,
     if_cuda = if_cuda,
+    py_binary = native.py_binary,
     py_library = _py_library,
     requirement = _requirement,
     requires_cuda_enabled = requires_cuda_enabled,

tools/codegen/build.bzl

@@ -8,3 +8,9 @@ def define_targets(rules):
         ],
         visibility = ["//visibility:public"],
     )
+
+    rules.py_binary(
+        name = "gen",
+        srcs = [":codegen"],
+        visibility = ["//visibility:public"],
+    )