user: implement mlibc as the libc, finally.

It's finally done..

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

user/include/mlibc/options/linux/generic/sys-pidfd.cpp

@@ -0,0 +1,40 @@
+#include <bits/ensure.h>
+#include <errno.h>
+#include <mlibc/debug.hpp>
+#include <mlibc/linux-sysdeps.hpp>
+#include <sys/pidfd.h>
+
+int pidfd_open(pid_t pid, unsigned int flags) {
+	auto sysdep = MLIBC_CHECK_OR_ENOSYS(mlibc::sys_pidfd_open, -1);
+	int fd = 0;
+
+	if(int e = sysdep(pid, flags, &fd); e) {
+		errno = e;
+		return -1;
+	}
+
+	return fd;
+}
+
+pid_t pidfd_getpid(int fd) {
+	auto sysdep = MLIBC_CHECK_OR_ENOSYS(mlibc::sys_pidfd_getpid, -1);
+	pid_t pid = 0;
+
+	if(int e = sysdep(fd, &pid); e) {
+		errno = e;
+		return -1;
+	}
+
+	return pid;
+}
+
+int pidfd_send_signal(int pidfd, int sig, siginfo_t *info, unsigned int flags) {
+	auto sysdep = MLIBC_CHECK_OR_ENOSYS(mlibc::sys_pidfd_send_signal, -1);
+
+	if(int e = sysdep(pidfd, sig, info, flags); e) {
+		errno = e;
+		return -1;
+	}
+
+	return 0;
+}