user: implement mlibc as the libc, finally.

It's finally done..

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

user/include/mlibc/tests/glibc/error_message_count.c

@@ -0,0 +1,13 @@
+#include <assert.h>
+#include <errno.h>
+#include <error.h>
+
+int main() {
+	assert(error_message_count == 0);
+	error(0, EINVAL, "test error #1");
+	assert(error_message_count == 1);
+	error_at_line(0, EINVAL, __FILE__, __LINE__, "test error #2");
+	assert(error_message_count == 2);
+
+	return 0;
+}