fix(CMSIS): Declare libc function stubs as weak

[MaureenHelm]

Declares _getpid() and _kill() function stubs as weak to avoid conflicting with similar function stubs defined in zephyr libc-hooks. This fixes linker errors when building zephyr with newlib on max32 boards.

Reported in zephyrproject-rtos/zephyr#73606

Hotfix applied to downstream fork in zephyrproject-rtos/hal_adi#1

Tested locally with Zephyr:

$ twister -p max32690evkit/max32690/m4 -T tests/lib/cpp/ -T tests/lib/c_lib/

And in Zephyr CI: https://github.com/zephyrproject-rtos/zephyr/actions/runs/9332489979

Checklist Before Requesting Review

• [x] PR Title follows correct guidelines.
• [x] Description of changes and all other relevant information.
• [x] (Optional) Link any related GitHub issues using a keyword
• [x] (Optional) Provide info on any relevant functional testing/validation. For API changes or significant features, this is not optional.