ps/output.c: include <dlfcn.h> only when necessary
dlopen() functionality is only used when SELinux support is enabled, so <dlfcn.h> only needs to be included when ENABLE_LIBSELINUX is defined. This fixes the build in configurations where <dlfcn.h> is not available.
Signed-off-by: Thomas Petazzoni thomas.petazzoni@free-electrons.com