Fix build errors under FreeBSD
Makefile.am: top.c was enlisted as Linux-only source, though it is
required for conky on every operating system.
conky.[ch]: top_running definition was inside #ifdef __linux__, though
required by top.c on every operating system.
freebsd.c: Change return type of update_*() to int, as required by
common.h; remove free_all_processes() as it is defined by top.c. The
changes done to freebsd.c must be done to netbsd.c and openbsd.c, too.
I did not do it as I have no opportunity to test conky under NetBSD or
OpenBSD.
Signed-off-by: Alexander Graf <agraf@znc.in>