Change jump targets in JMP_TBL from blocks to X86.JumpDest.

Authored by AndreasK on May 30 2018, 7:40 PM.

Description

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

Reviewers: bgamari

Reviewed By: bgamari

Subscribers: thomie, carter

GHC Trac Issues: Trac #15104

Differential Revision: https://phabricator.haskell.org/D4595