zephyr_cc_library: Move GCC specific flags to toolchain Moves GCC_ARM_C_FLAGS & _GCC_PICOLIBC_FLAGS out of the zephyr_cc_library definition and into the toolchain definitions instead. Change-Id: I6a8a21d984ce256e5279b47dd436c7b308a5ca32 Reviewed-on: https://pigweed-review.googlesource.com/c/zephyr/zephyr-bazel/+/435153