user: implement mlibc as the libc, finally.

It's finally done..

Signed-off-by: kaguya <vpshinomiya@protonmail.com>

user/include/mlibc/options/linux/generic/linux-unistd.cpp

@@ -0,0 +1,38 @@
+#include <bits/linux/linux_unistd.h>
+#include <bits/ensure.h>
+
+#include <errno.h>
+#include <mlibc/posix-sysdeps.hpp>
+#include <mlibc/linux-sysdeps.hpp>
+#include <unistd.h>
+
+int dup3(int oldfd, int newfd, int flags) {
+	if(oldfd == newfd) {
+		errno = EINVAL;
+		return -1;
+	}
+	MLIBC_CHECK_OR_ENOSYS(mlibc::sys_dup2, -1);
+	if(int e = mlibc::sys_dup2(oldfd, flags, newfd); e) {
+		errno = e;
+		return -1;
+	}
+	return newfd;
+}
+
+int vhangup(void) {
+	__ensure(!"Not implemented");
+	__builtin_unreachable();
+}
+
+int getdtablesize(void){
+	return sysconf(_SC_OPEN_MAX);
+}
+
+int syncfs(int fd) {
+	MLIBC_CHECK_OR_ENOSYS(mlibc::sys_syncfs, -1);
+	if(int e = mlibc::sys_syncfs(fd); e) {
+		errno = e;
+		return -1;
+	}
+	return 0;
+}