runtime: push arena on AIX higher due to clashes

Change-Id: I1bb7a0472e2e08a4bb2191e5434d1374c236a65a
Reviewed-on: https://go-review.googlesource.com/99117
Reviewed-by: Ian Lance Taylor <iant@golang.org>
diff --git a/libgo/go/runtime/malloc.go b/libgo/go/runtime/malloc.go
index 1405a54..c8d5284 100644
--- a/libgo/go/runtime/malloc.go
+++ b/libgo/go/runtime/malloc.go
@@ -308,9 +308,9 @@
 				p = uintptr(i)<<40 | uintptrMask&(0x0040<<32)
 			case GOOS == "aix":
 				if i == 0 {
-					p = uintptrMask&(1<<32) | uintptrMask&(0xa0<<52)
+					p = uintptrMask&(1<<42) | uintptrMask&(0xa0<<52)
 				} else {
-					p = uintptr(i)<<32 | uintptrMask&(0x70<<52)
+					p = uintptr(i)<<42 | uintptrMask&(0x70<<52)
 				}
 			default:
 				p = uintptr(i)<<40 | uintptrMask&(0x00c0<<32)