user: implement mlibc as the libc, finally.

It's finally done..

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

user/include/mlibc/tests/posix/open_memstream.c

@@ -0,0 +1,65 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <assert.h>
+
+#define WRITE_NO 1024
+
+int main() {
+	size_t size;
+	char *buf;
+
+	FILE *fp = open_memstream(&buf, &size);
+	assert(fp);
+
+	char c = 'A';
+	for (size_t i = 0; i < WRITE_NO; i++)
+		assert(fwrite(&c, sizeof(char), 1, fp) == 1);
+
+	// Flush the file to update the pointers.
+	assert(!fflush(fp));
+
+	assert(size == WRITE_NO);
+	for (size_t i = 0; i < size; i++)
+		assert(buf[i] == c);
+
+	// Check if the stream maintains a null-bye at the end.
+	assert(buf[size] == '\0');
+
+	// Stream should be expanded, size should be == 2*WRITE_NO.
+	assert(!fseek(fp, WRITE_NO, SEEK_END));
+	assert(!fflush(fp));
+	assert(size == 2*WRITE_NO);
+	assert(buf[size] == '\0');
+
+	// Check if it's filled with zero's.
+	for (size_t i = WRITE_NO; i < size; i++)
+		assert(buf[i] == '\0');
+
+	// Go back and overwrite the 0's with 'B'.
+	assert(!fseek(fp, -WRITE_NO, SEEK_CUR));
+	c = 'B';
+	for (size_t i = 0; i < WRITE_NO; i++)
+		assert(fwrite(&c, sizeof(char), 1, fp) == 1);
+
+	// Check if that happened.
+	assert(size == 2*WRITE_NO);
+	for (size_t i = WRITE_NO; i < size; i++)
+		assert(buf[i] == c);
+	assert(buf[size] == '\0');
+
+	// Go to the front and write 'B'.
+	assert(!fseek(fp, 0, SEEK_SET));
+	for (size_t i = 0; i < WRITE_NO; i++)
+		assert(fwrite(&c, sizeof(char), 1, fp) == 1);
+
+	// Check if that happened.
+	assert(size == 2*WRITE_NO);
+	for (size_t i = 0; i < size; i++)
+		assert(buf[i] == c);
+	assert(buf[size] == '\0');
+
+	// Close the file, we have tested everything.
+	assert(!fclose(fp));
+	free(buf);
+	return 0;
+}