syscall: fix mkall.sh for nacl

TBR=adg
CC=golang-dev
https://golang.org/cl/2208050

src/pkg/syscall/mkall.sh

@@ -137,7 +137,7 @@ nacl_386)
 	NACL="/home/rsc/pub/nacl/native_client"
 	NACLRUN="$NACL/src/trusted/service_runtime"
 	NACLSDK="$NACL/src/third_party/nacl_sdk/linux/sdk/nacl-sdk/nacl"
-	mksyscall="./mksyscall.sh -l32"
+	mksyscall="./mksyscall.sh -l32 -nacl"
 	mksysnum="./mksysnum_nacl.sh $NACLRUN/include/bits/nacl_syscalls.h"
 	mktypes="godefs -gsyscall -f-m32 -f-I$NACLSDK/include -f-I$NACL"
 	mkerrors="./mkerrors_nacl.sh $NACLRUN/include/sys/errno.h"