Use llvm_asm! instead of deprecated asm!

[kennystrawnmusic]

Fixes #107

This potentially breaks users on older nightlies.

[phil-opp]

Thank you!

[phil-opp]

Published as v0.9.2

[JakkuSakura]

   Compiling bootloader v0.9.19 (/Users/jack/.cargo/registry/src/github.com-1ecc6299db9ec823/bootloader-0.9.19)
warning: use of deprecated macro `llvm_asm`: will be removed from the compiler, use asm! instead
  --> src/main.rs:45:5
   |
45 |     llvm_asm!("call $1; ${:private}.spin.${:uid}: jmp ${:private}.spin.${:uid}" ::
   |     ^^^^^^^^
   |
   = note: `#[warn(deprecated)]` on by default

warning: use of deprecated macro `llvm_asm`: will be removed from the compiler, use asm! instead
  --> src/main.rs:91:5
   |
91 |     llvm_asm!("mov bx, 0x0
   |     ^^^^^^^^

warning: `bootloader` (bin "bootloader") generated 2 warnings

Why is this happening?

[bjorn3]

llvm_asm!() is now deprecated. In it's place a new asm!() syntax has been created. The original asm!() macro was renamed to llvm_asm!() before the new asm!() macro was introduced. Basically the migration path from the old to the new asm syntax is: asm!() renamed to llvm_asm!(). New asm!() introduced. llvm_asm!() deprecated. (current step) And then in the future removing llvm_asm!(). Bootloader will need to be updated to the new asm!() syntax before the old syntax is removed. This has already been done for the 0.10 series in #154, but the 0.9 series still uses llvm_asm!().