Add some symlink tests to runtime

[jeremyd2019]

In msys2/msys2-runtime#254 (comment) I made a quick test to prove the current behavior of the deepcopy symlink type, and @dscho fleshed that out into something more automated in the linked comment. Thinking about trying to improve that deepcopy code more, I started thinking including tests of as much of the symlink behavior as possible would be helpful.

So far, I've thrown together this shell script to make all the objects I know how to create.

#!/bin/bash -e

# needs: coreutils openbsd-netcat

mkdir menagerie && cd menagerie

echo "this is a regular file" > file
mkdir dir
mknod block b 8 0
mknod char c 1 3
mkfifo fifo

# making a socket isn't as straightforward
(timeout 0.1 nc -klU socket || test $? -eq 124 && test -S socket)

# make a directory junction using cmd, since I don't think there's a cygwin
# way to do it
cmd //c "mklink /j dirjunction dir"

for wsym in lnk sys nativestrict deepcopy; do
	for dst in file dir dirjunction block char fifo socket; do
		MSYS=winsymlinks:${wsym} ln -s ${dst} ${dst}${wsym}
	done
done