eglibc-external: don't run ${CC} at parse time

Signed-off-by: Christopher Larson <chris_larson@mentor.com>
libgcc-external: dep on libc

Signed-off-by: Christopher Larson <chris_larson@mentor.com>
gcc-runtime-external: dep on libc

Signed-off-by: Christopher Larson <chris_larson@mentor.com>