Newer LLVM makes memset recursive

[tari]

I've discovered that recent rustc nightlies (since January 30 at least) are smart enough to optimize memset and possibly other functions provided here into calls to the corresponding intrinsic which makes them recurse infinitely.

I'm guessing it's related to the switch to LLVM 3.8 in 303892ee15. I'm adopting a workaround with optimized assembly versions of these functions which are opaque to the optimizer, but that's not a portable nor particularly good solution.

[alexcrichton]

Hm, I wonder if the #![no_builtins] attribute was somehow broken as part of that upgrade? Or maybe it's a bug in LLVM? Not sure...

[tari]

Oh, I failed to notice #![no_builtins] so my code (using these implementations) didn't have it.

I compiled rlibc (rather than my own code) with the same compiler and that doesn't seem to happen, so it's a problem on my end. Sorry for the noise!