ucm: include sys/wait.h to fix build on Android

ucm: include sys/wait.h to fix build on Android

    src/ucm/main.c:788:8: error: implicit declaration of function 'WIFSIGNALED' is invalid in C99 [-Werror,-Wimplicit-function-declaration]
                        if (WIFSIGNALED(err)) {
                            ^
    src/ucm/main.c:790:10: error: implicit declaration of function 'WIFEXITED' is invalid in C99 [-Werror,-Wimplicit-function-declaration]
                        } if (WIFEXITED(err)) {
                              ^
    src/ucm/main.c:791:34: error: implicit declaration of function 'WEXITSTATUS' is invalid in C99 [-Werror,-Wimplicit-function-declaration]
                                if (ignore_error == false && WEXITSTATUS(err) != 0) {

Signed-off-by: Chih-Wei Huang <cwhuang@linux.org.tw>
Signed-off-by: Jaroslav Kysela <perex@perex.cz>