Solaris' GCC can't understand that our use is fine, unlike modern compilers:
```
list.c: In function 'print_totals_basic':
list.c:1191:4: error: format not a string literal, argument types not checked [-Werror=format-nonliteral]
  uint64_to_str(totals.files, 0));
  ^~~~~~~~~~~~~
cc1: all warnings being treated as errors
```

It's presumably because of older gettext missing format attributes.

Inspired by RsyncProject/rsync@3f2a38b.

It runs on Solaris 5.11 via a VirtualBox VM.

Solaris' sed appears broken and chokes on the old version:
```
running build-aux/version.sh
chunk 1 (sed)
5
7
0
alpha
chunk 2 (sed + tr)
5|7|0|alpha|
chunk 3 (sed + tr + sed)
chunk 4 (sed + tr + sed + tr)
```

vs (good):
```
running build-aux/version-gsed.sh
chunk 1 (gsed)
5
7
0
alpha
chunk 2 (gsed + tr)
5|7|0|alpha|
chunk 3 (gsed + tr + gsed)
5.7.0alpha
chunk 4 (gsed + tr + gsed + tr)
5.7.0alpha
```

Rather than requiring GNU sed, rewrite in POSIX awk. Thank you to Kerin
Millar for the rewrite.

Unfortunately, we cannot rely on the xpg4 POSIX versions, because of:
"""
Only the core-os packages are guaranteed to be present on a Solaris 11
regular installation, thus only oawk/awk and nawk are there. In particular,
when you create a new non global zone, it contains by default the
solaris-small-server group package so neither the xpg4 nor the gnu awk
binaries are available.
"""

As a bonus, it's IMO far more legible now. Given Recent Events, the fewer
immediately-obvious sed expressions in the world, the better.

Thanks-to: Kerin Millar <[email protected]>

On NetBSD:
```
  In file included from common/common.h:17,
                   from common/common.c:12:
  ../../src/common/tuklib_integer.h:69: error: "bswap16" redefined [-Werror]
     69 | # define bswap16(n) __builtin_bswap16(n)
        |
  In file included from /usr/include/amd64/bswap.h:13,
                   from /usr/include/sys/endian.h:107,
                   from /usr/include/amd64/endian.h:3,
                   from /usr/include/sys/types.h:98,
                   from /usr/include/stdlib.h:41,
                   from ../../src/common/sysdefs.h:134,
                   from common/common.h:15,
                   from common/common.c:12:
  /usr/include/sys/bswap.h:71: note: this is the location of the previous definition
     71 | #define bswap16(x) \
        |
```

If we're in the case where we know we have __builtin_bswap*, just undef
_bswap* first.