Squid with netfilter-conntrack and libcap (missing) - tcp_outgoing_mark

I'm trying to compile squid with netfilter-conntrack and libcap in order to be able to use "tcp_outgoing_mark".

I added:

--with-netfilter-conntrack \
--with-libcap \

to the Makefile of squid.

Unfortunately, while compiling the package squid, I'm always getting the error

configure: Support for Netfilter-based interception proxy requested: yes
configure: WARNING: Missing needed capabilities (libcap 2.09+) for TPROXY
configure: WARNING: Linux Transparent Proxy (version 4+) support WILL NOT be enabled
configure: WARNING: Reduced support to NAT Interception Proxy
configure: error: Linux netfilter conntrack requires libcap support (libcap 2.09+)

I already compiled the package libcap via make -j5 V=sc package/libcap/compile, but the error continues when I execute:

make -j 5 V=sc package/squid/compile.

Is there something which I'm missing?

I'm also getting the message:

configure: libcap support enabled: no
configure: libcap2 headers are ok: no