Migrate code to new asm! syntax

[dreamer]

I was hoping to experiment with this repo a little bit to see if I could use Rust for implementing new built-in DOS commands for dosbox-staging, but ATM it does not compile.

Nightly transitioned to new asm! syntax; old syntax can still be used via llvm_asm! (but somehow it does not work for me), but perhaps it would be better to move to new syntax right away.

rust-lang/rust#70173
rust-lang/rust#68404

Right now, the code fails to compile with several errors like this one:

error: the legacy LLVM-style asm! syntax is no longer supported
 --> src/dos/io.rs:4:9
  |
4 |           asm!("xorl %eax, %eax
  |           ^---
  |           |
  |  _________help: replace with: `llvm_asm!`
  | |
5 | |               inb  %dx,  %al"
6 | |              : "={al}"(ret)
7 | |              : "{dx}"(port)
8 | |             );
  | |______________^
  |
  = note: consider migrating to the new asm! syntax specified in RFC 2873
  = note: alternatively, switch to llvm_asm! to keep your code working as it is

[o8vm]

Thanks for the report. I think I'm going to move the asm! macro to llvm_asm! once and then to the new asm!.

[o8vm]

New asm syntax is supported, and the build environment has been redesigned. This issue has been fixed and the build is now easier. If the issue persists, please open a new issue.