fix(interrupts): add preserves_flags option

`IF` from `EFLAGS` must not be restored upon exiting the asm block.
https://doc.rust-lang.org/stable/reference/inline-assembly.html#rules-for-inline-assembly

Signed-off-by: Martin Kröning <martin.kroening@eonerc.rwth-aachen.de>

src/instructions/interrupts.rs

@@ -19,7 +19,7 @@ pub fn enable() {
     // Otherwise, the compiler is free to move
     // reads and writes through this asm block.
     unsafe {
-        asm!("sti", options(nostack));
+        asm!("sti", options(preserves_flags, nostack));
     }
 }
 
@@ -32,7 +32,7 @@ pub fn disable() {
         // Omit `nomem` to imitate a lock acquire.
         // Otherwise, the compiler is free to move
         // reads and writes through this asm block.
-        asm!("cli", options(nostack));
+        asm!("cli", options(preserves_flags, nostack));
     }
 }