BuildSystem: Move all userpace libraries under the userspace directory

As the number of libraries is increasing, root directory starts to
expand. This adds better organization for libraries

userspace/libraries/LibC/dirent.cpp

@@ -0,0 +1,84 @@
+#include <dirent.h>
+#include <errno.h>
+#include <fcntl.h>
+#include <stdlib.h>
+#include <sys/syscall.h>
+#include <unistd.h>
+
+struct __DIR
+{
+	int fd { -1 };
+	size_t entry_count { 0 };
+	size_t entry_index { 0 };
+	// FIXME: we should probably allocate entries dynamically
+	//        based if syscall returns ENOBUFS
+	dirent entries[128];
+};
+
+int closedir(DIR* dirp)
+{
+	if (dirp == nullptr || dirp->fd == -1)
+	{
+		errno = EBADF;
+		return -1;
+	}
+
+	close(dirp->fd);
+	free(dirp);
+
+	return 0;
+}
+
+int dirfd(DIR* dirp)
+{
+	if (dirp == nullptr || dirp->fd == -1)
+	{
+		errno = EINVAL;
+		return -1;
+	}
+
+	return dirp->fd;
+}
+
+DIR* fdopendir(int fd)
+{
+	DIR* dirp = (DIR*)malloc(sizeof(DIR));
+	if (dirp == nullptr)
+		return nullptr;
+
+	dirp->fd = fd;
+	dirp->entry_count = 0;
+	dirp->entry_index = 0;
+
+	return dirp;
+}
+
+DIR* opendir(const char* dirname)
+{
+	int fd = open(dirname, O_RDONLY);
+	if (fd == -1)
+		return nullptr;
+	return fdopendir(fd);
+}
+
+struct dirent* readdir(DIR* dirp)
+{
+	if (dirp == nullptr || dirp->fd == -1)
+	{
+		errno = EBADF;
+		return nullptr;
+	}
+
+	dirp->entry_index++;
+	if (dirp->entry_index < dirp->entry_count)
+		return &dirp->entries[dirp->entry_index];
+
+	long entry_count = syscall(SYS_READ_DIR, dirp->fd, dirp->entries, sizeof(dirp->entries) / sizeof(dirp->entries[0]));
+	if (entry_count <= 0)
+		return nullptr;
+
+	dirp->entry_count = entry_count;
+	dirp->entry_index = 0;
+
+	return &dirp->entries[0];
+}