[Bug #21497] [ruby/socket]: add full prototype
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	otherwise, gcc 15 will complain:

	> init.c:573:19: error: too many arguments to function ‘Rconnect’; expected 0, have 3
	>   573 |     return (VALUE)Rconnect(arg->fd, arg->sockaddr, arg->len);
	>       |                   ^~~~~~~~ ~~~~~~~
	> In file included from init.c:11:
	> rubysocket.h:294:5: note: declared here
	>   294 | int Rconnect();
	>       |     ^~~~~~~~

	> sockssocket.c:33:9: error: too many arguments to function ‘SOCKSinit’; expected 0, have 1
	>    33 |         SOCKSinit("ruby");
	>       |         ^~~~~~~~~ ~~~~~~
	> In file included from sockssocket.c:11:
	> rubysocket.h:293:6: note: declared here
	>   293 | void SOCKSinit();
	>       |      ^~~~~~~~~

	Signed-off-by: Z. Liu <zhixu.liu@gmail.com>

Again, rsock_raise_socket_error is called only when getaddrinfo and getaddrname fail

Socket::ResolutionError#error_code returns Socket::EAI_XXX

[Bug #19012]

man recvmsg(2) states:

> Return Value
> These calls return the number of bytes received, or -1 if an error occurred.
> The return value will be 0 when the peer has performed an orderly shutdown.

Not too sure how one is supposed to make the difference between a packet of
size 0 and a closed connection.

* Windows: Fix warning about undefined if_indextoname()

* Windows: Fix UNIXSocket on MINGW and make .pair more reliable

* Windows: Use nonblock=true for read tests with scheduler

* Windows: Move socket detection from File.socket? to File.stat

Add S_IFSOCK to Windows and interpret reparse points accordingly.
Enable tests that work now.

* Windows: Use wide-char functions to UNIXSocket

This fixes behaviour with non-ASCII characters.
It also fixes deletion of temporary UNIXSocket.pair files.

* Windows: Add UNIXSocket tests for specifics of Windows impl.

* Windows: fix VC build due to missing _snwprintf

Avoid usage of _snwprintf, since it fails linking ruby.dll like so:

  linking shared-library x64-vcruntime140-ruby320.dll
  x64-vcruntime140-ruby320.def : error LNK2001: unresolved external symbol snwprintf
  x64-vcruntime140-ruby320.def : error LNK2001: unresolved external symbol vsnwprintf_l

whereas linking miniruby.exe succeeds.

This patch uses snprintf on the UTF-8 string instead.

Also remove branch GetWindowsDirectoryW, since it doesn't work.

* Windows: Fix dangling symlink test failures

Co-authored-by: Lars Kanis <kanis@comcard.de>

[Misc #18891]

Co-authored-by: Bruno Sutic <code@brunosutic.com>

Add connect_timeout to TCPSocket.new in the same way as Socket.tcp.

Closes [Feature #17187]