core-util: Avoid warnings when missing certain system calls

core-util: Avoid warnings when missing certain system calls

on systems lacking #defines HAVE_ACCEPT4, HAVE_PIPE2, SOCK_CLOEXEC

pulsecore/core-util.c: In function 'pa_open_cloexec':
pulsecore/core-util.c:3348:1: warning: label 'finish' defined but not used [-Wunused-label]
pulsecore/core-util.c: In function 'pa_socket_cloexec':
pulsecore/core-util.c:3370:1: warning: label 'finish' defined but not used [-Wunused-label]
pulsecore/core-util.c: In function 'pa_pipe_cloexec':
pulsecore/core-util.c:3393:1: warning: label 'finish' defined but not used [-Wunused-label]
pulsecore/core-util.c: In function 'pa_accept_cloexec':
pulsecore/core-util.c:3415:1: warning: label 'finish' defined but not used [-Wunused-label]

Signed-off-by: Peter Meerwald <pmeerw@pmeerw.net>