Import global_asm macro which now lives under core::arch

Author: phil-opp

src/main.rs

@@ -10,8 +10,7 @@ compile_error!("The bootloader crate must be compiled for the `x86_64-bootloader
 extern crate rlibc;
 
 use bootloader::bootinfo::{BootInfo, FrameRange};
-use core::convert::TryInto;
-use core::panic::PanicInfo;
+use core::{arch::global_asm, convert::TryInto, panic::PanicInfo};
 use core::{mem, slice};
 use fixedvec::alloc_stack;
 use usize_conversions::usize_from;