Include the fx_importer from upstream in IREE compiler API builds. (#16276)

We've started to get contributions upstream and I would like to remove
the forked code. This was designed to be re-exported from IREE, so just
following through on that.

I've added tests for both the onnx importer and fx that validate that we
indeed have them available, even if their dependencies aren't met.
diff --git a/compiler/bindings/python/CMakeLists.txt b/compiler/bindings/python/CMakeLists.txt
index 8c58b36..cc85f8a 100644
--- a/compiler/bindings/python/CMakeLists.txt
+++ b/compiler/bindings/python/CMakeLists.txt
@@ -141,6 +141,7 @@
     ADD_TO_PARENT IREEPythonSources
     ROOT_DIR "${IREE_SOURCE_DIR}/third_party/torch-mlir/python/torch_mlir"
     SOURCES
+      extras/fx_importer.py
       extras/onnx_importer.py
   )
 
diff --git a/compiler/bindings/python/test/CMakeLists.txt b/compiler/bindings/python/test/CMakeLists.txt
index 91d87d5..6f6cdb9 100644
--- a/compiler/bindings/python/test/CMakeLists.txt
+++ b/compiler/bindings/python/test/CMakeLists.txt
@@ -5,5 +5,6 @@
 # SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 add_subdirectory(api)
+add_subdirectory(extras)
 add_subdirectory(ir)
 add_subdirectory(tools)
diff --git a/compiler/bindings/python/test/extras/CMakeLists.txt b/compiler/bindings/python/test/extras/CMakeLists.txt
new file mode 100644
index 0000000..18469dd
--- /dev/null
+++ b/compiler/bindings/python/test/extras/CMakeLists.txt
@@ -0,0 +1,21 @@
+# Copyright 2024 The IREE Authors
+#
+# Licensed under the Apache License v2.0 with LLVM Exceptions.
+# See https://llvm.org/LICENSE.txt for license information.
+# SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+
+if(IREE_INPUT_TORCH)
+  iree_py_test(
+    NAME
+      fx_importer_test
+    SRCS
+      "fx_importer_test.py"
+  )
+
+  iree_py_test(
+    NAME
+      onnx_importer_test
+    SRCS
+      "onnx_importer_test.py"
+  )
+endif()
diff --git a/compiler/bindings/python/test/extras/fx_importer_test.py b/compiler/bindings/python/test/extras/fx_importer_test.py
new file mode 100644
index 0000000..e6bfd13
--- /dev/null
+++ b/compiler/bindings/python/test/extras/fx_importer_test.py
@@ -0,0 +1,18 @@
+# Copyright 2024 The IREE Authors
+#
+# Licensed under the Apache License v2.0 with LLVM Exceptions.
+# See https://llvm.org/LICENSE.txt for license information.
+# SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+
+try:
+    from iree.compiler.extras import fx_importer
+except ModuleNotFoundError as e:
+    while e is not None:
+        if isinstance(e, ModuleNotFoundError) and e.name == "torch":
+            break
+        e = e.__cause__
+    else:
+        raise ModuleNotFoundError(
+            "Failed to import the fx_importer (for a reason other than torch "
+            "not being found)"
+        ) from e
diff --git a/compiler/bindings/python/test/extras/onnx_importer_test.py b/compiler/bindings/python/test/extras/onnx_importer_test.py
new file mode 100644
index 0000000..f06c81a
--- /dev/null
+++ b/compiler/bindings/python/test/extras/onnx_importer_test.py
@@ -0,0 +1,18 @@
+# Copyright 2024 The IREE Authors
+#
+# Licensed under the Apache License v2.0 with LLVM Exceptions.
+# See https://llvm.org/LICENSE.txt for license information.
+# SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+
+try:
+    from iree.compiler.extras import onnx_importer
+except ModuleNotFoundError as e:
+    while e is not None:
+        if isinstance(e, ModuleNotFoundError) and e.name == "onnx":
+            break
+        e = e.__cause__
+    else:
+        raise ModuleNotFoundError(
+            "Failed to import the fx_importer (for a reason other than onnx "
+            "not being found)"
+        ) from e
diff --git a/third_party/torch-mlir b/third_party/torch-mlir
index 1bf7614..26c0ecd 160000
--- a/third_party/torch-mlir
+++ b/third_party/torch-mlir
@@ -1 +1 @@
-Subproject commit 1bf7614165d8b9ae051b65ff337ec447a2a0e958
+Subproject commit 26c0ecd09c532204b80e2145bcbe1539238e4c33