Cross-compilation with Python bindings: PYO3_CROSS_LIB_DIR not set

[alphaville]

Describe the bug

When compiling with

.with_target_system("rpi").with_build_python_bindings()

the following error is produced

Must provide PYO3_CROSS_LIB_DIR environment variable when cross-compiling

To Reproduce

Complete example

import sys
import os
import casadi.casadi as cs
import opengen as og

optimizers_dir = "my_optimizers"
optimizer_name = "rosenbrock"

def get_open_local_absolute_path():
    cwd = os.getcwd()
    return cwd.split('open-codegen')[0]

nu, np = 5, 2
u = cs.SX.sym("u", nu)  # decision variable (nu = 5)
p = cs.SX.sym("p", 2)  # parameter (np = 2)
phi = og.functions.rosenbrock(u, p) + 1500*cs.sum1(u)

# c_f1 = cs.vertcat(p[0] * u[0] - u[1], p[1]*u[2] - u[3] + 0.1)
c_f2 = cs.vertcat(0.2 + 1.5 * u[0] - u[1], u[2] - u[3] - 0.1)

bounds = og.constraints.Ball2(None, 1.5)
problem = og.builder.Problem(u, p, phi) \
    .with_penalty_constraints(c_f2)\
    .with_constraints(bounds)
meta = og.config.OptimizerMeta()\
    .with_optimizer_name(optimizer_name)
build_config = og.config.BuildConfiguration() \
    .with_build_directory(optimizers_dir) \
    .with_build_mode(og.config.BuildConfiguration.DEBUG_MODE) \
    .with_open_version(local_path=get_open_local_absolute_path()) \
    .with_tcp_interface_config().with_target_system("rpi").with_build_python_bindings()
solver_cfg = og.config.SolverConfiguration() \
    .with_preconditioning(True)

builder = og.builder.OpEnOptimizerBuilder(problem,
                                          meta,
                                          build_config,
                                          solver_cfg)
builder.build()

System information

Tested on Linux and MacOS