user: implement mlibc as the libc, finally.

It's finally done..

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

user/include/mlibc/tests/posix/readv-writev.c

@@ -0,0 +1,53 @@
+#include <assert.h>
+#include <fcntl.h>
+#include <string.h>
+#include <unistd.h>
+#include <sys/uio.h>
+
+#ifdef USE_HOST_LIBC
+#define TEST_FILE "readv-writev-host-libc.tmp"
+#else
+#define TEST_FILE "readv-writev.tmp"
+#endif
+
+int main() {
+	// Make sure that it wasn't created by a previous test run
+	unlink(TEST_FILE);
+
+	int fd = open(TEST_FILE, O_RDWR | O_CREAT, 0644);
+	assert(fd != -1);
+
+	char str0[] = "hello ";
+	char str1[] = "world!";
+
+	struct iovec bufs[2] = {
+		{
+			.iov_base = &str0,
+			.iov_len = strlen(str0),
+		},
+		{
+			.iov_base = &str1,
+			.iov_len = strlen(str1),
+		},
+	};
+
+	ssize_t written = writev(fd, bufs, 2);
+	assert(written == 12);
+
+	memset(&str0, 0, strlen(str0));
+	memset(&str1, 0, strlen(str1));
+
+	assert(!lseek(fd, 0, SEEK_SET));
+
+	ssize_t read = readv(fd, bufs, 2);
+	assert(read == 12);
+
+	assert(!strncmp(str0, "hello ", 7));
+	assert(!strncmp(str1, "world!", 7));
+
+	assert(!close(fd));
+
+	unlink(TEST_FILE);
+
+	return 0;
+}