After this change the build fails on Solaris when compiled with Solaris Studio 12.3 compiler (GCC is OK on Linux and Solaris, Clang is OK on Linux and FreeBSD):
```
/opt/solarisstudio12.3/bin/cc -O -DHAVE_CONFIG_H  -I./missing  -D_U_="" -I. -I/opt/csw/include  -I/usr/local/include -I./missing -DINET6 -I/usr/inet6/include -g -c ./tcpdump.c
"ip.h", line 139: identifier redeclared: UNALIGNED
        current : struct ip_timestamp {unsigned char ipt_code, unsigned char ipt_len, unsigned char ipt_ptr, unsigned char ipt_oflwflg, union ipt_timestamp {..} ipt_timestamp}
        previous: struct ip {unsigned char ip_vhl, unsigned char ip_tos, unsigned short ip_len, unsigned short ip_id, unsigned short ip_off, unsigned char ip_ttl, unsigned char ip_p, unsigned short ip_sum, struct in_addr {..} ip_src, struct in_addr {..} ip_dst} : "ip.h", line 67
cc: acomp failed for ./tcpdump.c
*** Error code 2
```