build: make nacl pass

Add nacl.bash, the NaCl version of all.bash.
It's a separate script because it builds a variant of package syscall
with a large zip file embedded in it, containing all the input files
needed for tests.

Disable various tests new since the last round, mostly the ones using os/exec.

Fixes #7945.

LGTM=dave
R=golang-codereviews, remyoudompheng, dave, bradfitz
CC=golang-codereviews
https://golang.org/cl/100590044
diff --git a/test/nosplit.go b/test/nosplit.go
index 20f4f9b..35aa510 100644
--- a/test/nosplit.go
+++ b/test/nosplit.go
@@ -1,5 +1,7 @@
 // run
 
+// +build !nacl
+
 // Copyright 2014 The Go Authors.  All rights reserved.
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
@@ -273,7 +275,6 @@
 
 		ioutil.WriteFile(filepath.Join(dir, "asm.s"), buf.Bytes(), 0666)
 
-
 		cmd := exec.Command("go", "build")
 		cmd.Dir = dir
 		output, err := cmd.CombinedOutput()