add musl headers

libc/include/generic-musl/linux/string.h

@@ -0,0 +1,8 @@
+/* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */
+#ifndef _LINUX_STRING_H_
+#define _LINUX_STRING_H_
+
+/* We don't want strings.h stuff being used by user stuff by accident */
+
+#include <string.h>
+#endif /* _LINUX_STRING_H_ */