Compiler cannot include C++ headers when both PICOLIBC and LIB_CPLUSPLUS options are set

[r2r0]

Describe the bug
When CONFIG_PICOLIBC and CONFIG_LIB_CPLUSPLUS options are set at the same time then compiler is not able to include C++ headers i.e. cstdint.
When there is used picolib without enableing usage of C++ standard library then everything works well.
After adding CONFIG_LIB_CPLUSPLUS standard C++ headers cannot be found (see log below).

To Reproduce
Steps to reproduce the behavior:
Enable picolibc
Enable C++
Enable C++ standard library

Expected behavior
If C++ standard library cannot be used with picolib then this should be blocked at the kconfig level, otherwise compilation should succeed.

Impact
Showstopper for switching from newlib to picolib.

Logs and console output

ccache /opt/zephyr-sdk/arm-zephyr-eabi/bin/arm-zephyr-eabi-g++ ......
In file included from /home/hid/aurora/app/src/low_power/wakeup_button.cpp:18:
/home/hid/aurora/app/../shared/src/std_def.h:10:10: fatal error: cstdint: No such file or directory
   10 | #include <cstdint>
      |          ^~~~~~~~~

Environment (please complete the following information):

• OS: Linux
• Toolchain Zephyr SDK 0.15.2
• Commit SHA 27ec69e

Additional context
C++ related config:

CONFIG_PICOLIBC=y
CONFIG_CPLUSPLUS=y
CONFIG_STD_CPP17=y
CONFIG_LIB_CPLUSPLUS=y
CONFIG_CPP_MAIN=y

[stephanosio]

Using libstdc++ with picolibc requires the toolchains (i.e. Zephyr SDK) to include the picolibc, which is not currently the case.

The upcoming Zephyr SDK 0.16.0 release will include picolibc and the libstdc++ compiled for it: see #49922 (comment).

[r2r0]

Thanks a lot for a prompt answer.
Do you think that it would be a good idea to not allow users to select this combination of options for now?