File.Writer `splatByteAll` with high `splat` value is slow on Windows

[ilmaria]

Zig Version

0.15.0-dev.1438+242102f9d

Steps to Reproduce and Observed Behavior

Filling a file with zeroes with splatByteAll writes one byte at a time and is very slow.

pub fn main() !void {
    const out_file = try std.fs.cwd().createFile("output", .{ .truncate = true });
    var buf: [4096]u8 = @splat(0);
    var w = out_file.writer(&buf);
    try w.interface.splatByteAll(0, 100_000_000);
}

const std = @import("std");

Expected Behavior

I expected splatByteAll to use the writer buffer and write as many bytes at a time as possible.