user: implement mlibc as the libc, finally.

It's finally done..

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

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

@@ -0,0 +1,29 @@
+#include <string.h>
+#include <assert.h>
+
+int main() {
+	char buf[4];
+
+	// stpncpy
+	assert(stpncpy(buf, "", 4) == buf);
+	assert(!strcmp(buf, ""));
+	
+	assert(stpncpy(buf, "123", 4) == buf + 3);
+	assert(!strcmp(buf, "123"));
+	
+	assert(stpncpy(buf, "12", 4) == buf + 2);
+	assert(buf[0] == '1' && buf[1] == '2' && buf[2] == '\0' && buf[3] == '\0');
+
+	assert(stpncpy(buf, "123456", 4) == buf + 4);
+	assert(buf[0] == '1' && buf[1] == '2' && buf[2] == '3' && buf[3] == '4');
+
+	// stpcpy
+	assert(stpcpy(buf, "") == buf);
+	assert(!strcmp(buf, ""));
+	
+	assert(stpcpy(buf, "12") == buf + 2);
+	assert(!strcmp(buf, "12"));
+	
+	assert(stpcpy(buf, "123") == buf + 3);
+	assert(!strcmp(buf, "123"));
+}