compile with python 3.13t (nogil)

I have installed free-threading python 3.13 following https://py-free-threading.github.io/installing_cpython/ on ubuntu 22.04(with gcc 11.04.0), with command:

`conda create -n nogil --override-channels -c conda-forge python-freethreading`

But compile python 3.13t with boost-1.86.0 failed, below the steps:

1, configure boost successfully:
`./bootstrap.sh --with-python=/home/mydesktop/anaconda3/envs/nogil`

2, compile boost failed:
`./b2 --toolset=gcc --with-python include="/home/mydesktop/anaconda3/envs/nogil/include/python3.13t/" --with-thread --with-date_time --with-chrono --with-system`
3, error message:
```
`gcc.compile.c++ bin.v2/libs/python/build/gcc-11/release/x86_64/link-static/python-3.13/threading-multi/visibility-hidden/dict.o
In file included from ./boost/python/detail/prefix.hpp:13,
from ./boost/python/dict.hpp:8,
from libs/python/src/dict.cpp:4:
./boost/python/detail/wrap_python.hpp:57:11: fatal error: pyconfig.h: No such file or directory
57 | # include
| ^~~~~~~~~~~~
compilation terminated.

"g++" -fvisibility-inlines-hidden -m64 -pthread -O3 -finline-functions -Wno-inline -Wall -fvisibility=hidden -DBOOST_ALL_NO_LIB=1 -DBOOST_COBALT_USE_STD_PMR=1 -DBOOST_PYTHON_SOURCE -DBOOST_PYTHON_STATIC_LIB -DNDEBUG -I"." -I"/home/subaochen/anaconda3/envs/nogil/include/python3.13" -I"/home/subaochen/anaconda3/envs/nogil/include/python3.1t" -c -o "bin.v2/libs/python/build/gcc-11/release/x86_64/link-static/python-3.13/threading-multi/visibility-hidden/dict.o" "libs/python/src/dict.cpp"

...failed gcc.compile.c++ bin.v2/libs/python/build/gcc-11/release/x86_64/link-static/python-3.13/threading-multi/visibility-hidden/dict.o...
gcc.compile.c++ bin.v2/libs/python/build/gcc-11/release/x86_64/link-static/python-3.13/threading-multi/visibility-hidden/str.o
In file included from ./boost/python/detail/prefix.hpp:13,
from ./boost/python/str.hpp:8,
from libs/python/src/str.cpp:4:
./boost/python/detail/wrap_python.hpp:57:11: fatal error: pyconfig.h: No such file or directory
57 | # include
| ^~~~~~~~~~~~
compilation terminated.
```

Obviously I missed "pyconfig.h", but i successfully compiled boost 1.86 with python 3.11 with the same step. Any suggestions? Thanks in advance!

Start with the reported ./bootstrap.sh and ./b2 commands and inspect the generated include paths in the compiler output. Check boost/python/detail/wrap_python.hpp and the Python 3.13t include directory for pyconfig.h; done means Boost.Python compiles successfully with the free-threading Python installation.

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