V code: Use predefined argc, not argv.length

v/bin/make-icns.vx

@@ -144,7 +144,7 @@ def pack_icon_file
 	return pack_one( icon_type => data )
 }
 
-if const icons = argv[ 1 -> argv.length ] map pack_icon_file then
+if const icons = argv[ 1 -> argc ] map pack_icon_file then
 {
 	OUT <== pack_one( icns: icons )
 

v/bin/sha256sum-parallel.vx

@@ -1,6 +1,6 @@
 #!/usr/bin/env vx
 
-const args = argv[ 1 -> argv.length ]
+const args = argv[ 1 -> argc ]
 
 const results = channel()
 

v/bin/tcpcat.vx

@@ -1,6 +1,6 @@
 #!/usr/bin/env vx -Z
 
-if argv.length < 3 then
+if argc < 3 then
 {
 	warn "Usage:  tcpcat <host> <port>"
 	exit 2

v/examples/rot13.vx

@@ -1,6 +1,6 @@
 #!/usr/bin/env vx
 
-const args = argv[ 1 -> argv.length ]
+const args = argv[ 1 -> argc ]
 
 var text = join( " ", *args )