RP2040 cannot be compiled with C11 enabled

[ThadHouse]

Describe the bug
When compiling a project targeting RP2040 and C11 enabled, errors occur because both assert.h (from the std lib) and config_autogen.h (from zephyr) define static_assert as a macro, with the one in config_autogen not being guarded.

To Reproduce
Steps to reproduce the behavior:

1. Set C11 flag on any project (set_property(TARGET tgt PROPERTY C_STANDARD 11))
2. mkdir build; cd build
3. cmake -DBOARD=rpi_pico
4. make
5. See error

Expected behavior
No compiler error

Impact
C11 cannot be used for RP2040 projects

Environment (please complete the following information):

• OS: Linux and Windows
• Toolchain: Zephyr SDK 0.15.0
• Zephyr 3.1 (Still occurs in 3.2)

[cfriedt]

Building Zephyr for C11 should likely involve using a Kconfig option rather than setting a CMake property in an arbitrary CMakeLists.txt, but this should be investigated in any case.

A Kconfig value such as CONFIG_LIBC_STD_C11 or something along those lines would probably be smart.

[stephanosio]

Building Zephyr for C11 should likely involve using a Kconfig option rather than setting a CMake property in an arbitrary CMakeLists.txt, but this should be investigated in any case.

A Kconfig value such as CONFIG_LIBC_STD_C11 or something along those lines would probably be smart.

@cfriedt I would suggest moving that discussion to #45776 since this issue does not really have much to do with C language support in Zephyr.