Add --time-t-size option to print the size of time_t in bits

[fxlb]

Have tests/TESTrun run "./tcpdump --time-t-size and set HAVE_TIME_T_64
key based on that.

This will permit to run tests based on time_t size (32-bit or 64-bit).

Also:

Add eight time test files with packet dates in 2038, 2039, 2106 and 2107

Each capture file contains one packet.

time_2038.pcap: 2038-01-01 00:00:00
time_2038_max.pcap: 2038-01-19 03:14:07
time_2038_overflow.pcap: 2038-01-19 03:14:08
time_2039.pcap: 2039-01-01 00:00:00
time_2106.pcap: 2106-01-01 00:00:00
time_2106_max.pcap: 2106-02-07 06:28:15
time_2106_overflow.pcapng: 2106-02-07 06:28:16
time_2107.pcapng: 2107-01-01 00:00:00

The packet time when > 2038-01-19T03:14:07Z cannot be correctly printed
if time_t size is 32 bits (overflow).
Some tests are run only if HAVE_TIME_T_64 is set. it depends on the
output of "./tcpdump --time-t-size" (32 or 64).

A 32-bit unsigned time_t goes until 2106-02-07T06:28:15Z.
All values above require a pcapng file.

[fxlb]

Test on linux-armv7l with autoconf 2.72.
libpcap: Add AC_SYS_YEAR2038_RECOMMENDED in configure.ac. ./configure shows: checking size of time_t... 8
tcpdump: Add AC_SYS_YEAR2038_RECOMMENDED in configure.ac. ./configure shows: checking size of time_t... 8.
tcpdump --version shows: 32-bit build, 64-bit time_t
make check shows: 0 tests failed

(In libpcap, AC_SYS_LARGEFILE can be remove if AC_SYS_YEAR2038_RECOMMENDED is added.)

Tested also with libpcap version 1.10.5 and tcpdump version 4.99.5 (same patch): 0 tests failed

$ ./tcpdump --version
tcpdump version 4.99.5
libpcap version 1.10.5 (with TPACKET_V3)
OpenSSL 3.0.2 15 Mar 2022
SMI-library: 0.4.8
32-bit build, 64-bit time_t

[fxlb]

Test on linux-mips with autoconf 2.72.
libpcap: Add AC_SYS_YEAR2038_RECOMMENDED in configure.ac. ./configure shows:
checking for gcc option to enable large file support... -D_FILE_OFFSET_BITS=64
checking for gcc option for timestamps after 2038... support not detected
configure: error: in '/home/buildbot-worker/tmp/libpcap':
configure: error: could not enable timestamps after mid-January 2038.
This package recommends support for these later
timestamps. However, to proceed with signed 32-bit
time_t even though it will fail then, configure with
'--disable-year2038'.

$ apt list libc6-dev
libc6-dev/oldoldstable,now 2.28-10+deb10u1 mips [installed,automatic]

2.28 < 2.34, minimal version to support the preprocessor macro _TIME_BITS (to have support with -D_TIME_BITS=64).

[infrastation]

For reference, MC includes a lot in the --version output, because it is also a project with a long history of portability:

GNU Midnight Commander 4.8.28
Built with GLib 2.80.3
Built with S-Lang 2.2.4 with terminfo database
With builtin Editor
With subshell support as default
With support for background operations
With mouse support on xterm
With internationalization support
With multiple codepages support
Virtual File Systems:
 cpiofs, tarfs, sfs, extfs, ftpfs, fish
Data types:
 char: 8; int: 32; long: 32; void *: 32; size_t: 32; off_t: 64;

[fxlb]

(After this PR more steps are needed for Y2038-safety.)