test: enable bug385_32 test on amd64p32.

LGTM=dave
R=dave, rsc
CC=golang-codereviews
https://golang.org/cl/78110043
diff --git a/test/fixedbugs/bug385_32.go b/test/fixedbugs/bug385_32.go
index 4c3cad7..daf2a08 100644
--- a/test/fixedbugs/bug385_32.go
+++ b/test/fixedbugs/bug385_32.go
@@ -1,4 +1,4 @@
-// +build 386 arm
+// +build 386 amd64p32 arm
 // errorcheck
 
 // Copyright 2011 The Go Authors.  All rights reserved.