user: implement mlibc as the libc, finally.

It's finally done..

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

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

@@ -0,0 +1,16 @@
+#ifndef _GNU_SOURCE
+#define _GNU_SOURCE
+#endif
+#include <assert.h>
+#include <string.h>
+
+int main() {
+	char test[19] = "Hello mlibc World!";
+	char *alloca_ed = strdupa(test);
+	assert(!strcmp(test, alloca_ed));
+
+	char *trimmed = strndupa(test, 5);
+	assert(!strcmp("Hello", trimmed));
+
+	return 0;
+}