tests: cpp: cxx: Test with various types of libc
tests: cpp: cxx: Test with various types of libc

This commit changes the C++ subsystem test, which previously was only
being run with the minimal libc, to be run with all the mainstream C
libraries (minimal libc, newlib, newlib-nano, picolibc).

Signed-off-by: Stephanos Ioannidis <dc76e9f0c0006e8f919e0c515c66dbba3982f785@stephanos.io>

galak/zephyr,finikorg/zephyr,zephyrproject-rtos/zephyr,galak/zephyr,galak/zephyr,zephyrproject-rtos/zephyr,finikorg/zephyr,galak/zephyr,finikorg/zephyr,finikorg/zephyr,zephyrproject-rtos/zephyr,zephyrproject-rtos/zephyr,finikorg/zephyr,zephyrproject-rtos/zephyr,galak/zephyr