user: implement mlibc as the libc, finally.

It's finally done..

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

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

@@ -0,0 +1,21 @@
+#include <assert.h>
+#include <stdbool.h>
+#include <stdio.h>
+#include <errno.h>
+#include <error.h>
+
+bool ran = false;
+
+void test_progname(void) {
+	ran = true;
+	fprintf(stderr, "progname test");
+}
+
+int main() {
+	assert(error_print_progname == NULL);
+	error_print_progname = &test_progname;
+	error(0, EINVAL, "test error #1");
+	assert(ran == true);
+
+	return 0;
+}