How to check if a target supports posix

Help
1

How can I check in my code if I can run std.posix functions?
Or do you just have to check if the OS is linux, macos, bsd, etc.

2

this is the logic std.posix uses

const use_libc = builtin.link_libc or switch (native_os) {
    .windows, .wasi => true,
    else => false,
};

/// A libc-compatible API layer.
pub const system = if (use_libc)
    std.c
else switch (native_os) {
    .linux => linux,
    .plan9 => std.os.plan9,
    .psp => struct {
        pub const fd_t = i32;
        pub const pid_t = void;
        pub const pollfd = void;
        pub const uid_t = void;
        pub const gid_t = void;
        pub const mode_t = u32;
        pub const nlink_t = u32;
        pub const blksize_t = u32;
        pub const ino_t = u64;
        pub const IFNAMESIZE = {};
        pub const SIG = void;

        // https://github.com/pspdev/newlib/blob/9e0a073634ad73e8e088f2e071c55a9fe5d39709/newlib/libc/sys/psp/sys/dirent.h#L19
        pub const NAME_MAX = 255;
    },
    else => struct {
        pub const pid_t = void;
        pub const pollfd = void;
        pub const fd_t = void;
        pub const uid_t = void;
        pub const gid_t = void;
        pub const mode_t = u0;
        pub const nlink_t = u0;
        pub const blksize_t = void;
        pub const ino_t = void;
        pub const IFNAMESIZE = {};
        pub const SIG = void;
    },
};