x64: use constant pool for u64 constants rather than movabs. (#4088)

* Allow emitting u64 constants into constant pool.

* Use constant pool for constants on x64 that do not fit in a simm32 and are needed as a RegMem or RegMemImm.

* Fix rip-relative addressing bug in pinsrd emission.

cranelift/codegen/src/isa/s390x/lower/isle.rs

@@ -17,7 +17,7 @@ use crate::{
         StackSlot, TrapCode, Value, ValueList,
     },
     isa::unwind::UnwindInst,
-    machinst::{InsnOutput, LowerCtx},
+    machinst::{InsnOutput, LowerCtx, VCodeConstant, VCodeConstantData},
 };
 use std::boxed::Box;
 use std::cell::Cell;