Improved toolchain / libc handling

[tejlmand]

Is your enhancement proposal related to a problem? Please describe.
PR #12393 introduced the TOOLCHAIN_HAS_NEWLIB CMake variable being used for twister filtering.
The PR #36140 introduced export of this symbol into Kconfig.

The issue should improve consistency in Zephyr toolchain handling by using actual TOOLCHAIN_HAS_<library> to ensure better dependency handling for toolchains as well as consistency in Zephyr build system configurations.

Describe the solution you'd like
The exported TOOLCHAIN_HAS_<lib> should be used by Kconfig:

zephyr/cmake/modules/kconfig.cmake

Line 131 in ef203fd

TOOLCHAIN_HAS_NEWLIB=$<IF:$<BOOL:${TOOLCHAIN_HAS_NEWLIB}>,y,n>

Describe alternatives you've considered
In toolchain WG it has been discussed if it would be possible and feasible to extend toolchain testing from basic compile flag testing to feature based testing, such as linker flag testing or libc / newlib / picolibc testing.

Such toolchain can be seen as further improvement, as having a TOOLCHAIN_HAS_<lib> infrastructure in place in Kconfig doesn't impact how that information is obtained (by fixed CMake setting or obtained through toolchain testing).

Additional context

[zephyrbot]

Hi @tejlmand,

This issue, marked as an Enhancement, was opened a while ago and did not get any traction. Please confirm the issue is correctly assigned and re-assign it otherwise.

Please take a moment to review if the issue is still relevant to the project. If it is, please provide feedback and direction on how to move forward. If it is not, has already been addressed, is a duplicate, or is no longer relevant, please close it with a short comment explaining the reason.

Thanks!