Change jump targets in JMP_TBL from blocks to X86.JumpDest.
Jump tables always point to blocks when we first generate them. However
there are rare situations where we can shortcut one of these blocks to a
static address during the asm shortcutting pass.
While we already updated the data section accordingly this patch also
extends this to the references stored in JMP_TBL.
Test Plan: ci
Reviewed By: bgamari
Subscribers: thomie, carter
GHC Trac Issues: Trac #15104
Differential Revision: https://phabricator.haskell.org/D4595