[llvm] r206228 - [ARM64][MC] Set the default CPU string to generic.

[Tim Northover]

> In the case of the C API, I think it's better to have a hard line.  It's a
> stable API.  It shouldn't be broken.

So we can never again change the default CPU on any target because
some user of the C API may be relying on it? That *is* insane, and I
strongly oppose a move in that direction.

As I understand it, you're still getting the code you ask for, just a
less efficient version of it.

> In the future, I would hope that such changes are reverted until a proper
> fix is in place.

Patches welcome.

Tim.