assert.h should not include non libc headers

[yonsch]

Describe the bug
If a source file includes the standard assert.h header, it also includes non standard Zephyr specific headers, as the assertions use printk, which includes logging.
In my case, a HAL source file included assert.h, and ended up also including the following files (in order):

zephyr/lib/libc/minimal/include/assert.h
zephyr/include/sys/__assert.h
zephyr/include/sys/printk.h
zephyr/include/logging/log.h
zephyr/include/logging/log_core.h
zephyr/include/logging/log_msg.h
zephyr/include/sys/util.h

And so a non Zephyr source file ended up "contaminated" with Zephyr definitions. One such definition was the KHZ macro, which conflicted with a definition of the same name in the HAL.

Expected behavior
In my opinion, standard library headers should not rely on non standard headers, or at least should be extra careful about including such headers.

Impact
Definitions ending up in a source file not expecting them (HAL) can cause redefinition warnings, with a possibility of the wrong definitions being chosen.
Another possible case is a definition coincidentally having the same name as a symbol in a source file. If we're unlucky, the symbol would be quietly substituted, possibly causing a bug.

Environment (please complete the following information):

• OS: Linux
• Toolchain: 0.13.1
• Commit SHA or Version used: boards: Add support for the raspberrypi pico #34835

[nashif]

this should have been kept as a bug, but regardless, the issue was resolved in 786647b