LibCore: Make Core::System::pipe2() available on Lagom

Note that this drops the flags on the floor if not on linux or serenity.

Userland/Libraries/LibCore/System.cpp

@@ -45,14 +45,6 @@ ErrorOr<void> unveil(StringView path, StringView permissions)
     HANDLE_SYSCALL_RETURN_VALUE("unveil"sv, rc, {});
 }
 
-ErrorOr<Array<int, 2>> pipe2(int flags)
-{
-    Array<int, 2> fds;
-    if (::pipe2(fds.data(), flags) < 0)
-        return Error::from_syscall("pipe2"sv, -errno);
-    return fds;
-}
-
 ErrorOr<void> sendfd(int sockfd, int fd)
 {
     if (::sendfd(sockfd, fd) < 0)
@@ -709,4 +701,17 @@ ErrorOr<void> socketpair(int domain, int type, int protocol, int sv[2])
     return {};
 }
 
+ErrorOr<Array<int, 2>> pipe2([[maybe_unused]] int flags)
+{
+    Array<int, 2> fds;
+#if defined(__unix__)
+    if (::pipe2(fds.data(), flags) < 0)
+        return Error::from_syscall("pipe2"sv, -errno);
+#else
+    if (::pipe(fds.data()) < 0)
+        return Error::from_syscall("pipe2"sv, -errno);
+#endif
+    return fds;
+}
+
 }

Userland/Libraries/LibCore/System.h

@@ -27,7 +27,6 @@ namespace Core::System {
 #ifdef __serenity__
 ErrorOr<void> pledge(StringView promises, StringView execpromises = {});
 ErrorOr<void> unveil(StringView path, StringView permissions);
-ErrorOr<Array<int, 2>> pipe2(int flags);
 ErrorOr<void> sendfd(int sockfd, int fd);
 ErrorOr<int> recvfd(int sockfd, int options);
 ErrorOr<void> ptrace_peekbuf(pid_t tid, void const* tracee_addr, Bytes destination_buf);
@@ -85,6 +84,7 @@ ErrorOr<int> mkstemp(Span<char> pattern);
 ErrorOr<void> fchmod(int fd, mode_t mode);
 ErrorOr<void> rename(StringView old_path, StringView new_path);
 ErrorOr<void> utime(StringView path, Optional<struct utimbuf>);
+ErrorOr<Array<int, 2>> pipe2(int flags);
 
 ErrorOr<int> socket(int domain, int type, int protocol);
 ErrorOr<void> bind(int sockfd, struct sockaddr const*, socklen_t);