don't modify argv, use a counter

on some platforms (OpenBSD) this changes the exposed argv in tools
using the kvm_* interface, such as ps and pgrep.

arg.h

@@ -21,12 +21,13 @@ extern char *argv0;
 					argc--;\
 					break;\
 				}\
-				for (brk_ = 0, argv[0]++, argv_ = argv;\
-						argv[0][0] && !brk_;\
-						argv[0]++) {\
+				int i_;\
+				for (i_ = 1, brk_ = 0, argv_ = argv;\
+						argv[0][i_] && !brk_;\
+						i_++) {\
 					if (argv_ != argv)\
 						break;\
-					argc_ = argv[0][0];\
+					argc_ = argv[0][i_];\
 					switch (argc_)
 
 #define ARGEND			}\