Following approach suggested by @hpkfft.

Set the "-U,_PyClassMethod_New" linker flag on the Python library itself
isntead of on the CMAKE_MODULE_LINKER_FLAGS property.

Context:
https://github.com/llvm/llvm-project/pull/107103#discussion_r1925834532

This code is brittle, especially when called from a superproject that
adds the `nanobind-*` target in a different source directory:
```cmake
get_property(all_targets DIRECTORY ${CMAKE_CURRENT_SOURCE_DIR} PROPERTY BUILDSYSTEM_TARGETS)
```

The changes here do help with my downstream build, but I'm not sure if
using the `MLIR_DISABLE_CONFIGURE_PYTHON_DEV_PACKAGES` option introduced
in https://github.com/llvm/llvm-project/pull/117934 is the right fix
given that the option is currently scoped directly to one location with
a matching name:
https://github.com/llvm/llvm-project/blob/7ad8a3da4771ce8abbd146611124104d42a4e63e/mlir/cmake/modules/MLIRDetectPythonEnv.cmake#L4-L5

Some other solutions to consider:

1. Search through an explicit list of target names using `if (TARGET)`
2. Iterate over _all_ targets in the project, not just the targets in
the current directory, using code like
https://stackoverflow.com/a/62311397
3. Iterate over targets in the directory known to MLIR
(`llvm-project/mlir/python`)
4. Move this `target_compile_options` setup into
`mlir_configure_python_dev_packages` (I started on this, but that runs
into similar issues where the target is defined in a different
directory)

See https://cmake.org/cmake/help/latest/policy/CMP0175.html

> The `OUTPUT` form does not accept `PRE_BUILD`, `PRE_LINK`, or
`POST_BUILD` keywords.

When using CMake version 3.31+, this results in ~2000 lines of warning
spam in my downstream project:

```
CMake Warning (dev) at build-gcc/lib/cmake/mlir/AddMLIRPython.cmake:606 (add_custom_command):
  The following keywords are not supported when using
  add_custom_command(OUTPUT): PRE_BUILD.

  Policy CMP0175 is not set: add_custom_command() rejects invalid arguments.
  Run "cmake --help-policy CMP0175" for policy details.  Use the cmake_policy
  command to set the policy and suppress this warning.
Call Stack (most recent call first):
  build-gcc/lib/cmake/mlir/AddMLIRPython.cmake:222 (add_mlir_python_sources_target)
  build-gcc/lib/cmake/mlir/AddMLIRPython.cmake:256 (_process_target)
  compiler/bindings/python/CMakeLists.txt:239 (add_mlir_python_modules)
This warning is for project developers.  Use -Wno-dev to suppress it.
```

General docs:
https://cmake.org/cmake/help/latest/command/add_custom_command.html.
Note that `PRE_BUILD` only appears in the _second_ signature for the
function (which takes `TARGET`) not the first (which takes `OUTPUT`).

This PR allows the users to specify the `NB_DOMAIN` for
`add_mlir_python_extension`. This allows users to avoid nanobind domain
conflicts, when python bindings from multiple `mlir` projects were
imported.
(https://nanobind.readthedocs.io/en/latest/faq.html#how-can-i-avoid-conflicts-with-other-projects-using-nanobind)

Reland reverted https://github.com/llvm/llvm-project/pull/107103 with
the fixes for Python 3.8

cc @jpienaar

Co-authored-by: Peter Hawkins <phawkins@google.com>

Breaks on 3.8, rolling back to avoid breakage while fixing.

This reverts commit 9dee7c44491635ec9037b90050bcdbd3d5291e38.

Related to https://github.com/llvm/llvm-project/issues/105522

Description:

This PR is a joint work with Peter Hawkins (@hawkinsp) originally done
by myself for pybind11 and then reworked to nanobind based on Peter's
branch: https://github.com/hawkinsp/llvm-project/tree/nbdev .

- Added free-threading CPython mode support for MLIR Python bindings
- Added a test which can reveal data races when cpython and LLVM/MLIR
compiled with TSAN

Context:
- Related to https://github.com/google/jax/issues/23073

Co-authored-by: Peter Hawkins <phawkins@google.com>

`NanobindAdaptors.h` uses `PyClassMethod_New` to build `pure_subclass`es
but nanobind doesn't declare this API as undefined in its linker flags.
So we need to declare it as such for downstream users that do not do
something like `-undefined dynamic_lookup`