Error while building ZephyrOS-Firmeware with CMake/Ninja and CPLUSPLUS C++

Question

I want to build firmware with ZephyrOS for nRF52840. I set up the toolchain (on Windows) and everything works so far (Pyhton, West, CMake, Ninja..). I can even build most programs with "cmake -GNinja -DBOARD=nrf52840_pca10056".

But there is a problem with programs that need C++, which support is activated with "CONFIG_CPLUSPLUS=y" in Config-File (https://docs.zephyrproject.org/latest/reference/kconfig/CONFIG_CPLUSPLUS.html).

When I try to build the sample ("echo_server" sample vom samples/net/socket/echo_server) with "cmake -GNinja -DBOARD=nrf52840_pca10056 -DCONF_FILE="prj.conf overlay-ot.conf" .." eveything seams to work so far:

Fine: cmake -GNinja -DBOARD=nrf52840_pca10056 -DCONF_FILE="prj.conf overlay-ot.conf

But, when I then run "ninja" to create .hex-File I get an error:

Error: "The command ".\bootstrap" can not be found or is written wrong"

"FAILED: zephyr/ext_proj/STamp/ot/ot-bootstrap The command ".\bootstrap" can not be found or is written wrong No patch step for 'ot'" "

I think it has something to do with my Complier and/or C++ because when I change to "CONFIG_CPLUSPLUS=n" in the .conf-File, it builds the binaries without any errors. The problem is that without C++-support I can not use some features I want to use (Openthread) because they depend on C++.

I'm using GNU_ARM_Embedded_Toolchain (7-2018q2). I tried to install C++ runtime environments and some "Windows SDKs" but nothing happened.

C++ Runtime Environment

I work with Windows 10 and with Tools like in the Getting Started Guide from Zephyr (Python3, pip, west, Ninja, CMake). (https://docs.zephyrproject.org/latest/getting_started/index.html)

Hope you have some ideas, thanks for your help! With best regards

Sebastian