[Thumb-1] Fix corner cases for compressed jump tables

[Thumb-1] Fix corner cases for compressed jump tables

Summary:
When synthesized TBB/TBH is expanded, we need to avoid the case of:
   BaseReg is redefined after the load of branching target. E.g.:

    %R2 = tLEApcrelJT <jt#1>
    %R1 =  tLDRr %R1, %R2    ==> %R2 = tLEApcrelJT <jt#1>
    %R2 = tLDRspi %SP, 12        %R2 = tLDRspi %SP, 12
    tBR_JTr %R1                  tTBB_JT %R2, %R1
`
Reviewers: jmolloy

Reviewed By: jmolloy

Subscribers: llvm-commits, rengolin

Differential Revision: https://reviews.llvm.org/D32250

llvm-svn: 300870