Zephyr images can optionally use "newlib" libraries. These are not supported by YP. Provide support for "newlib" for all supported Zephyr toolchains (x86, ARM, ARC, IAMCU, Nios2...)
All supported toolchains should also contain "newlib", as "newlib" libc is selectable via "menuconfig". The build should support all available tunes for given toolchain.
Implemented in meta-zephyr: https://git.yoctoproject.org/cgit/cgit.cgi/meta-zephyr/commit/?id=c28b4eacf94efd90e9cb0488f7a232e5746e0174