runtime: push arena on AIX higher due to clashes

    
    Reviewed-on: https://go-review.googlesource.com/99117

From-SVN: r258337

gcc/go/gofrontend/MERGE

-2a07cd31927ac943104f55d2b696e53e7cd073b3
+112623c89ee42b42bc748f12d9c704615634501b
 
 The first line of this file holds the git revision number of the last
 merge done from the gofrontend repository.

libgo/go/runtime/malloc.go

@@ -308,9 +308,9 @@ func mallocinit() {
 				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)