Use std.os.windows.poll for std.posix.poll implementation rather than libc dependency

[mochalins]

std.posix.poll implementation incorrectly depends on libc on Windows, despite std.os.windows.poll existing. Issue similar to #9971, and resolved similar to #15225.

[andrewrk]

Thanks, looks good. How did you test it?

[mochalins]

Thanks, looks good. How did you test it?

I sanity-checked by running standard library tests on Linux, then ran zig-network's test suite using wine, with adjustments to use the POSIX poll on Windows (using zig build --zig-lib-dir) instead of ws2's select.

Without the patch (compilation failure due to requiring libc):

zig build test -Dtarget=x86_64-windows-gnu -fwine
test
└─ run test
   └─ zig test Debug x86_64-windows-gnu 1 errors
/home/***/Software/Install/lib/zig/std/c.zig:1840:12: error: dependency on libc must be explicitly specified in the build command
pub extern "c" fn poll(fds: [*]c.pollfd, nfds: c.nfds_t, timeout: c_int) c_int;
           ^~~
referenced by:
    poll: /home/***/Software/Install/lib/zig/std/posix.zig:6484:26
    waitForSocketEvent: network.zig:989:85
    1 reference(s) hidden; use '-freference-trace=3' to see all references
error: the following command failed with 1 compilation errors:
/home/***/Software/Install/bin/zig test -ODebug -target x86_64-windows-gnu -mcpu baseline --dep network -Mroot=/home/***/Projects/zig-network/testsuite.zig -Mnetwork=/home/***/Projects/zig-network/network.zig --cache-dir /home/***/Projects/zig-network/.zig-cache --global-cache-dir /home/***/.cache/zig --name test --listen=- 
Build Summary: 0/3 steps succeeded; 1 failed (disable with --summary none)
test transitive failure
└─ run test transitive failure
   └─ zig test Debug x86_64-windows-gnu 1 errors
error: the following build command failed with exit code 1:
/home/***/Projects/zig-network/.zig-cache/o/f04f1741572aaa666b5ce6df87305999/build /home/***/Software/Install/bin/zig /home/***/Projects/zig-network /home/***/Projects/zig-network/.zig-cache /home/***/.cache/zig --seed 0xa7d02b6f -Z13f5919b3699ea29 test -Dtarget=x86_64-windows-gnu -fwine

With the patch (all tests pass):

zig build --zig-lib-dir ../zig/lib test -Dtarget=x86_64-windows-gnu -fwine
test
└─ run test stderr
002c:fixme:winediag:loader_init wine-staging 9.5 is a testing version containing experimental patches.
002c:fixme:winediag:loader_init Please mention your exact version when filing bug reports on winehq.org.
142.250.76.142:80
[2404:6800:400a:805::200e]:80
Echo: Hi from socket!
0118:fixme:winsock:WSAIoctl SIO_UDP_CONNRESET stub
0118:fixme:winsock:WSAIoctl SIO_UDP_CONNRESET stub
0118:fixme:winsock:WSAIoctl SIO_UDP_CONNRESET stub

The branch used for testing this patch is here: https://github.com/mochalins/zig-network/tree/windows_poll