The minimal libc is currently built as a zephyr_library and will be
included in the final link line as such. However, the c_library property
will still be set as "-lc" (for most linkers) and will be added to the
link line. This effectively requires that a separate libc implementation
be available in the toolchain and makes it possible to accidentally pull
from the non-minimal libc.
This doesn't seem desirable, so try to prevent this by clearing the
c_library property if we are using the minimal libc.
Signed-off-by: Jonathon Penix <jpenix@quicinc.com>