add missing include to quieten compiler

libc/stdlib/secure_getenv.c

@@ -1,8 +1,7 @@
-
 #include <stdlib.h>
+#include <unistd.h>
 
 char *secure_getenv(const char *name) {
 	if (issetugid()) return NULL;
 	return getenv(name);
 }
-