[PPC64] Bug fix: when enabling sibling-call-opt and shrink-wrapping, the tail...

[PPC64] Bug fix: when enabling sibling-call-opt and shrink-wrapping, the tail call branch instruction might disappear

Bug Pattern:
    # BB#0:                                 # %entry
	    cmpldi	 3, 0
	    beq-	 0, .LBB0_2
    # BB#1:                                 # %exit
	    lwz 4, 0(3)
	    #TC_RETURNd8 LVComputationKind 0
    .LBB0_2:                                # %cond.false
	    mflr 0
	    std 0, 16(1)
	    stdu 1, -96(1)
    .Ltmp0:
	    .cfi_def_cfa_offset 96
    .Ltmp1:
	    .cfi_offset lr, 16
	    bl __assert_fail
	    nop

The branch instruction for tail call return is not generated, because the
shrink-wrapping pass choosing a new Restore Point: %cond.false, so %exit
block is not sent to emitEpilogue, that's why the branch is not generated.

Thanks Kit's opinions!
Reviewers: nemanjai hfinkel tjablin kbarton

http://reviews.llvm.org/D17606

llvm-svn: 265112