rustc nightlies break on any dependency that relies on parking_lot 0.9

[jdm]

error: legacy asm! syntax is no longer supported
  --> /root/.cargo/registry/src/github.com-1ecc6299db9ec823/parking_lot-0.9.0/src/elision.rs:70:13
   |
70 |               asm!("xacquire; lock; cmpxchgq $2, $1"
   |               ^---
   |               |
   |  _____________help: replace with: `llvm_asm!`
   | |
71 | |                  : "={rax}" (prev), "+*m" (self)
72 | |                  : "r" (new), "{rax}" (current)
73 | |                  : "memory"
74 | |                  : "volatile");
   | |_______________________________^
error: legacy asm! syntax is no longer supported
   --> /root/.cargo/registry/src/github.com-1ecc6299db9ec823/parking_lot-0.9.0/src/elision.rs:97:13
    |
97  |               asm!("xrelease; lock; xaddq $2, $1"
    |               ^---
    |               |
    |  _____________help: replace with: `llvm_asm!`
    | |
98  | |                  : "=r" (prev), "+*m" (self)
99  | |                  : "0" (val.wrapping_neg())
100 | |                  : "memory"
101 | |                  : "volatile");
    | |_______________________________^
error: aborting due to 2 previous errors
error: could not compile `parking_lot`.

This is a hard error in the compiler, not a warning that we can ignore. We can't upgrade our rustc nightly until we update beyond:

• winit 0.20 (https://github.com/Eijebong/servo/tree/winit)
• tokio-reactor 0.2

We can also remove the use of the nightly feature from layout_thread and layout_thread_2020 which allows the build to complete.

[SimonSapin]

If I remember correctly use of inline assembly is an optional optimization in parking_lot. Disabling it might be another option, if updating past 0.9 proves difficult.

[SimonSapin]

Ah sorry, you already wrote the same at the end of your message.