go.tools/ssa: fix ssa tests (fix build partly)

R=adonovan
CC=golang-dev
https://golang.org/cl/13668048

ssa/testdata/objlookup.go

@@ -90,6 +90,7 @@ func main() {
 	v9 := S{} // &v9::Alloc
 
 	v10 := &v9 // v10::Alloc &v9::Alloc
+	_ = v10    // v10::Alloc
 
 	var v11 *J = nil // v11::Const
 	v11.method()     // v11::Const
@@ -115,6 +116,7 @@ func main() {
 	}
 
 	for k, v := range m { // k::Extract v::Extract m::MakeMap
+		_ = k // k::Extract
 		v++   // v::BinOp
 	}
 
@@ -131,6 +133,7 @@ func main() {
 	ch := make(chan int) // ch::MakeChan
 	select {
 	case x := <-ch: // x::UnOp (receive) ch::MakeChan
+		_ = x // x::UnOp
 	}
 
 	// .Op is an inter-package FieldVal-selection.

ssa/testdata/valueforexpr.go

@@ -2,7 +2,7 @@
 
 package main
 
-// This file is the input to TestCanonicalPos in source_test.go, which
+// This file is the input to TestValueForExpr in source_test.go, which
 // ensures that each expression e immediately following a /*@kind*/(x)
 // annotation, when passed to Function.ValueForExpr(e), returns a
 // non-nil Value of the same type as e and of kind 'kind'.
@@ -14,9 +14,11 @@ func f(param int) {
 	ch := /*@MakeChan*/ (make(chan int))
 	/*@UnOp*/ (<-ch)
 	x := /*@UnOp*/ (<-ch)
+	_ = x
 	select {
 	case /*@Extract*/ (<-ch):
 	case x := /*@Extract*/ (<-ch):
+		_ = x
 	}
 	defer /*@Function*/ (func() {
 	})()
@@ -28,6 +30,7 @@ func f(param int) {
 	}
 	_ = /*@Phi*/ (y)
 	map1 := /*@MakeMap*/ (make(map[string]string))
+	_ = map1
 	_ = /*@MakeMap*/ (map[string]string{"": ""})
 	_ = /*@MakeSlice*/ (make([]int, 0))
 	_ = /*@MakeClosure*/ (func() { print(param) })