[mlir][python][cmake] Allow skipping nanobind compile options changes. (#123997)

Context:
#107103 (comment)

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 #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)

Author: ScottTodd

mlir/cmake/modules/AddMLIRPython.cmake

@@ -671,8 +671,11 @@ function(add_mlir_python_extension libname extname)
       ${ARG_SOURCES}
     )
 
-    if (LLVM_COMPILER_IS_GCC_COMPATIBLE OR CLANG_CL)
-      # Avoids warnings from upstream nanobind.
+    if (NOT MLIR_DISABLE_CONFIGURE_PYTHON_DEV_PACKAGES
+        AND (LLVM_COMPILER_IS_GCC_COMPATIBLE OR CLANG_CL))
+      # Avoid some warnings from upstream nanobind.
+      # If a superproject set MLIR_DISABLE_CONFIGURE_PYTHON_DEV_PACKAGES, let
+      # the super project handle compile options as it wishes.
       set(nanobind_target "nanobind-static")
       if (NOT TARGET ${nanobind_target})
         # Get correct nanobind target name: nanobind-static-ft or something else