test: Use global variables to defeat gccgo optimizer.

The gccgo compiler is smart enough to not make something which
is not used.  Use global variables to defeat this
optimization.

R=rsc
CC=golang-dev
https://golang.org/cl/2129041

test/fixedbugs/bug273.go

@@ -15,6 +15,8 @@ var bug = false
 var minus1 = -1
 var big int64 = 10 | 1<<32
 
+var g1 []int
+
 func shouldfail(f func(), desc string) {
 	defer func() { recover() }()
 	f()
@@ -26,52 +28,56 @@ func shouldfail(f func(), desc string) {
 }
 
 func badlen() {
-	_ = make([]int, minus1)
+	g1 = make([]int, minus1)
 }
 
 func biglen() {
-	_ = make([]int, big)
+	g1 = make([]int, big)
 }
 
 func badcap() {
-	_ = make([]int, 10, minus1)
+	g1 = make([]int, 10, minus1)
 }
 
 func badcap1() {
-	_ = make([]int, 10, 5)
+	g1 = make([]int, 10, 5)
 }
 
 func bigcap() {
-	_ = make([]int, 10, big)
+	g1 = make([]int, 10, big)
 }
 
 const (
 	addrBits = 8*uint(unsafe.Sizeof((*byte)(nil)))
 	sh = addrBits/2 - 2
 )
+var g2 [][1<<sh][1<<sh]byte
 func overflow() {
-	_ = make([][1<<sh][1<<sh]byte, 64)
+	g2 = make([][1<<sh][1<<sh]byte, 64)
 }
 
+var g3 map[int]int
 func badmapcap() {
-	_ = make(map[int]int, minus1)
+	g3 = make(map[int]int, minus1)
 }
 
 func bigmapcap() {
-	_ = make(map[int]int, big)
+	g3 = make(map[int]int, big)
 }
 
+var g4 chan int
 func badchancap() {
-	_ = make(chan int, minus1)
+	g4 = make(chan int, minus1)
 }
 
 func bigchancap() {
-	_ = make(chan int, big)
+	g4 = make(chan int, big)
 }
 
+var g5 chan [1<<15]byte
 func overflowchan() {
 	if addrBits == 32 {
-		_ = make(chan [1<<15]byte, 1<<20)
+		g5 = make(chan [1<<15]byte, 1<<20)
 	} else {
 		// cannot overflow on 64-bit, because
 		// int is 32 bits and max chan value size