libgo patch committed: Don't assume that _ = *s will panic if s is nil

[Ian Lance Taylor]

With the gc toolchain apparently
    var s *string
    _ = *s
is enough to panic with a nil pointer dereference. The gccgo compiler
will simply discard the dereference, which I think is a reasonable and
acceptable optimization. Change the tests to use an exported variable
instead. The tests are not currently run, but they will be with a
later patch to gotools.

Bootstrapped and ran Go testsuite on x86_64-pc-linux-gnu.  Committed
to mainline.

Ian

Index: gcc/go/gofrontend/MERGE
===================================================================
--- gcc/go/gofrontend/MERGE     (revision 249561)
+++ gcc/go/gofrontend/MERGE     (working copy)
@@ -1,4 +1,4 @@
-b5c9fe259ec43f8079581c3bea0f1d12d85213a7
+8804c912363320e0c229c5a471fb6f4b9e5965e6
 
 The first line of this file holds the git revision number of the last
 merge done from the gofrontend repository.
Index: libgo/go/runtime/testdata/testprog/crash.go
===================================================================
--- libgo/go/runtime/testdata/testprog/crash.go (revision 249205)
+++ libgo/go/runtime/testdata/testprog/crash.go (working copy)
@@ -13,6 +13,8 @@ func init() {
        register("Crash", Crash)
 }
 
+var NilPointer *string
+
 func test(name string) {
        defer func() {
                if x := recover(); x != nil {
@@ -21,8 +23,7 @@ func test(name string) {
                fmt.Printf(" done\n")
        }()
        fmt.Printf("%s:", name)
-       var s *string
-       _ = *s
+       *NilPointer = name
        fmt.Print("SHOULD NOT BE HERE")
 }
 
Index: libgo/go/runtime/testdata/testprogcgo/crash.go
===================================================================
--- libgo/go/runtime/testdata/testprogcgo/crash.go      (revision 249205)
+++ libgo/go/runtime/testdata/testprogcgo/crash.go      (working copy)
@@ -13,6 +13,8 @@ func init() {
        register("Crash", Crash)
 }
 
+var NilPointer *string
+
 func test(name string) {
        defer func() {
                if x := recover(); x != nil {
@@ -21,8 +23,7 @@ func test(name string) {
                fmt.Printf(" done\n")
        }()
        fmt.Printf("%s:", name)
-       var s *string
-       _ = *s
+       *NilPointer = name
        fmt.Print("SHOULD NOT BE HERE")
 }