socketpair: support pipe2 where available

By replacing pipe with pipe2, it would save us 4 extra system calls of
setting O_NONBLOCK and O_CLOEXEC. This system call is widely supported
across UNIX-like OS's: Linux, *BSD, and SunOS derivatives - Solaris,
illumos, etc.

Ref:
https://man7.org/linux/man-pages/man2/pipe.2.html
https://man.freebsd.org/cgi/man.cgi?query=pipe
https://man.dragonflybsd.org/?command=pipe2
https://man.netbsd.org/pipe.2
https://man.openbsd.org/pipe.2
https://docs.oracle.com/cd/E88353_01/html/E37841/pipe2-2.html
https://illumos.org/man/2/pipe2
https://www.gnu.org/software/gnulib/manual/html_node/pipe2.html

Closes #16987

configure.ac

@@ -577,7 +577,7 @@ AM_CONDITIONAL(BUILD_UNITTESTS, test x$supports_unittests = xyes)
 # In order to detect support of sendmmsg() and accept4(), we need to escape the POSIX
 # jail by defining _GNU_SOURCE or <sys/socket.h> will not expose it.
 case $host_os in
-  linux*)
+  linux*|cygwin*|msys*)
     CPPFLAGS="$CPPFLAGS -D_GNU_SOURCE"
     ;;
 esac
@@ -4124,6 +4124,7 @@ AC_CHECK_FUNCS([\
   gettimeofday \
   mach_absolute_time \
   pipe \
+  pipe2 \
   poll \
   sendmmsg \
   sendmsg \