C++ support in Zephyr

[alexanderwachter]

This is a tracking issue for C++ enhancements for Zephyr

Add any missing features, things that work and things that don't work here.

Missing features

List of missing features. The order defines the priority.

• Static local initialization. Static objects need to be guarded to get initialized properly (_cxa_guard* functions). PR exists: cpp: add support for function static initializers #19754
• syscalls for class methods
• std::mutex
• std::atomic
• std::thread

Things that don't work

• native_posix board behaves strange and does not terminate when compiled with gcov
• static objects (see missing feature)
• C++ standard library without exceptions. Exceptions getting enabled when the project links to the lib. Even with --fno-exceptions

Things that work

• Use C++ for App development with restrictions
• STL
• Exceptions

Nice to have

• exceptions with low footprint

[nashif]

@pabigot FYI

[pabigot]

@alexanderwachter could you perhaps update #18554 instead, and change its description to reflect "status as of 2.5"? We don't need multiple things tracking the gaps.

[abrodkin]

@evgeniy-paltsev @ruuddw FYI