Update include directory

libc/include/string.h

@@ -0,0 +1,20 @@
+#ifndef _STRING_H
+#define _STRING_H
+
+#include <stddef.h>
+
+#ifdef __cplusplus
+extern "C"
+{
+#endif
+
+    void *memcpy(void *, const void *, size_t);
+    void *memset(void *, int, size_t);
+    char *strcpy(char *, const char *);
+    size_t strlen(const char *);
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif