get correct getenv prototype instead of cooking one up that's not going
to be useless with recent compilers

--- a/getopt.c
+++ b/getopt.c
@@ -143,9 +143,7 @@
 /* Avoid depending on library functions or files
    whose names are inconsistent.  */
 
-#ifndef getenv
-extern char *getenv ();
-#endif
+#include <stdlib.h>
 
 #endif /* not __GNU_LIBRARY__ */