Use multilib concept with Clang/ATfE#2700

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rgrr wants to merge 12 commits intoraspberrypi:developfrom

rgrr:clang-corrections

Commits on Oct 16, 2025

use the same runtime_init() as for newlib -> picolibc now working for clang19.1.5/21.1.1
rgrr
committed

Commits on Oct 17, 2025

catch the case that PICO_CLIB is not set
rgrr
committed

Commits on Oct 30, 2025

now using multilib concept which makes everything much cleaner and clearer
rgrr
committed