cmd/5g etc: mechanical cleanup

Run rsc.io/grind rev 796d0f2 on C->Go conversions.

This replaces various awkward := initializations with plain var declarations.

Checked bit-for-bit compatibility with toolstash + buildall.

Change-Id: I601101d8177894adb9b0e3fb55dfe0ed4f544716
Reviewed-on: https://go-review.googlesource.com/6517
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
diff --git a/src/cmd/internal/gc/select.go b/src/cmd/internal/gc/select.go
index ca6a21d..4fbf826 100644
--- a/src/cmd/internal/gc/select.go
+++ b/src/cmd/internal/gc/select.go
@@ -11,7 +11,7 @@
 	var ncase *Node
 	var n *Node
 
-	def := (*Node)(nil)
+	var def *Node
 	lno := int(setlineno(sel))
 	count := 0
 	typechecklist(sel.Ninit, Etop)