The lack of this was causing PCAP_IS_SUITABLE to fail on Arch Linux, at
least. I think that in some cases this caused both -L../libpcap and
-lpcap to be added to the linker line, which could cause an error
because of the need to link with -lnl. (We check for -lnl when
--with-libpcap=included is used (since r23163), but the PCAP_IS_SUITABLE
failure went around this check and allowed linking with the included
libpcap without checking whether -lnl is required.)
Here are reported build failures and responses:
http://seclists.org/nmap-dev/2011/q3/449http://seclists.org/nmap-dev/2011/q4/33http://seclists.org/nmap-dev/2012/q1/369