runtime: fix lfstackUnpack on ia64

    
    The top three region number bits must be masked out before
    right-shifting the address bits into place, otherwise they will be
    copied down into the lower always-zero address bits.
    
    Reviewed-on: https://go-review.googlesource.com/84535

From-SVN: r257061

gcc/go/gofrontend/MERGE

-016ea21c4cba324c6ea6424da7988c6f985e671b
+553e04735d1be372c596c720bcaea27e050b13a6
 
 The first line of this file holds the git revision number of the last
 merge done from the gofrontend repository.

libgo/go/runtime/lfstack_64bit.go

@@ -78,7 +78,7 @@ func lfstackUnpack(val uint64) *lfnode {
 		return (*lfnode)(unsafe.Pointer(uintptr(int64(val) >> sparcLinuxCntBits << 3)))
 	}
 	if GOARCH == "ia64" {
-		return (*lfnode)(unsafe.Pointer(uintptr((val>>ia64CntBits<<3)&(1<<(64-3)-1) | val&^(1<<(64-3)-1))))
+		return (*lfnode)(unsafe.Pointer(uintptr(((val & (1<<(64-3) - 1)) >> ia64CntBits << 3) | val&^(1<<(64-3)-1))))
 	}
 	if GOARCH == "ppc64" && GOOS == "aix" {
 		if val&(1<<63) != 0 {