user: implement mlibc as the libc, finally.

It's finally done..

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

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

@@ -0,0 +1,25 @@
+#ifndef _GNU_SOURCE
+#define _GNU_SOURCE
+#endif
+#include <stdio.h>
+#include <string.h>
+#include <assert.h>
+
+int main () {
+	char str[] = "The Last Supper by Leonardo da Vinci";
+	char *str_temp;
+
+	// Test strstr
+	str_temp = strstr(str, "Supper"); /* Find a substring in the string */
+	assert(!strcmp(str_temp, "Supper by Leonardo da Vinci"));
+
+	/* Following calls use memory APIs for the above tasks */
+	// Test memchr
+	str_temp = (char *)memchr((void *)str, 'L', strlen(str));
+	assert(!strcmp(str_temp, "Last Supper by Leonardo da Vinci"));
+
+	// Test memrchr
+	str_temp = (char *)memrchr((void *)str, 'L', strlen(str));
+	assert(!strcmp(str_temp, "Leonardo da Vinci"));
+	return 0;
+}