Fixes the following build error where gcc fails because the
client/common does not exist yet:

  CC       shared/nm-utils/clients_common_libnmc_base_la-nm-enum-utils.lo
 cc1: error: ./clients/common: No such file or directory [-Werror]
 cc1: all warnings being treated as errors
 make[4]: *** [shared/nm-utils/clients_common_libnmc_base_la-nm-enum-utils.lo] Error 1
 #

 libtool: compile:  gcc -DHAVE_CONFIG_H -I. -I.. -I../shared -I./shared -I../libnm-core -I./libnm-core -I../libnm -I./libnm -I../clients/common -I./clients/common ... -c ../shared/nm-utils/nm-enum-utils.c  -fPIC -DPIC -o shared/nm-utils/.libs/clients_common_libnmc_base_la-nm-enum-utils.o
 cc1: error: ./clients/common: No such file or directory [-Werror]

Fixes: 34342618