Add reference types R32 and R64

-Add resumable_trap, safepoint, isnull, and null instructions
-Add Stackmap struct and StackmapSink trait

Co-authored-by: Mir Ahmed <mirahmed753@gmail.com>
Co-authored-by: Dan Gohman <sunfish@mozilla.com>

cranelift/codegen/src/isa/x86/binemit.rs

@@ -5,7 +5,7 @@ use super::registers::RU;
 use crate::binemit::{bad_encoding, CodeSink, Reloc};
 use crate::ir::condcodes::{CondCode, FloatCC, IntCC};
 use crate::ir::{Ebb, Function, Inst, InstructionData, JumpTable, Opcode, TrapCode};
-use crate::isa::{RegUnit, StackBase, StackBaseMask, StackRef};
+use crate::isa::{RegUnit, StackBase, StackBaseMask, StackRef, TargetIsa};
 use crate::regalloc::RegDiversions;
 
 include!(concat!(env!("OUT_DIR"), "/binemit-x86.rs"));