Rust triggers LLVM ARM backend bug

[sanxiyn]

Rust triggers LLVM bug 17180. I haven't figured out the exact condition yet, but using LLVM's integrated assembler is required, so this started to happen only when we switched to LLVM's integrated assembler from Android NDK's external assembler(#8931).

The bug is fixed upstream in r190417. Should I upgrade to the latest LLVM, or just cherry-pick the fix? The fix is trivial, so cherry-picking is not hard. @alexcrichton?

[alexcrichton]

Let's cherry-pick it for now. Assigning myself.

[alexcrichton]

For posterity, the cherry-pick doesn't cleanly apply, so @sanxiyn is going to resolve the conflicts and rebase it on our current llvm patch and I'll send a pull to integrate it.