cmd/compile: make Class a Stringer

Change-Id: I7fd137d01ab5a0690773ca6e47d2bd796f0e393e
Reviewed-on: https://go-review.googlesource.com/42177
Run-TryBot: Josh Bleecher Snyder <[email protected]>
Reviewed-by: Brad Fitzpatrick <[email protected]>
TryBot-Result: Gobot Gobot <[email protected]>

Author: josharian

src/cmd/compile/internal/gc/class_string.go

@@ -31,6 +31,7 @@ func isRuntimePkg(p *types.Pkg) bool {
 // called declaration contexts.
 type Class uint8
 
+//go:generate stringer -type=Class
 const (
 	Pxxx      Class = iota // no class; used during ssa conversion to indicate pseudo-variables
 	PEXTERN                // global variable