NaCl is not so much about executing C/C++ code as it is about executing native compiled binaries. This has issues:
It's incredible Google is even pushing this. It's so anti-portable and in concept anti-web.
There is a "portable" version of this, called "Portable Native Client". This means, of course, that NaCl is actually "Non-Portable Native Client" and that should itself be a clue. The "portable" version uses LLVM bitcode and a virtual machine. So more than a decade later, we've basically reinvented Java virtual machine applets minus the gigantic runtime (and language of your choice).
The only people who could possibly benefit from NaCl are Google. There's no general case use for this, and pushing it as standard into Chrome is a nasty move. Mozilla also reject the idea of NaCl. I believe Opera rejects it too (lacking a link). So, why is this being pushed?
The same is true of Ubuntu and the Multiverse. You can CHOOSE to run pay software, the same as Android. I can run a commercial server daemon on pure, fully open Linux. Does that cease to be Linux? No.
It's a matter of what's meant by "Linux". Everyone used to mean "GNU/Linux" when they said simply "Linux". Android isn't GNU/Linux. There's no GNU in it - they stripped out what they could and rewrote from scratch what they couldn't. It's Apache/BSD/Linux.
So no, Android is not "Linux" by the definition of what everyone - before Android came along - would call Linux.
We are not a clone.