[PPC] Remove isBarrier from CFENCE8's definition.

[timshen]

Summary

This is my misunderstanding on isBarrier. It's not for memory barriers,
but for other control flow purposes. lwsync doesn't have it either.

This fixes a simple crash with -verify-machineinstrs like below:

define void @Foo() {
entry:
  %tmp = load atomic i64, i64* undef acquire, align 8
  unreachable
}

I deliberately don't want to check in the test, since there is little
chance to regress on such a mistake. Such a test adds noise to the code
base.

I plan to check in first, since it fixes a crash, and the fix is obvious.

llvm/trunk/lib/Target/PowerPC/PPCInstr64Bit.td

def ADDISgotTprelHA: Pseudo<(outs g8rc:$rD), (ins g8rc_nox0:$reg, s16imm64:$disp),
                                                tglobaltlsaddr:$disp))]>,
                   isPPC64;
 def LDgotTprelL: Pseudo<(outs g8rc:$rD), (ins s16imm64:$disp, g8rc_nox0:$reg),
                         "#LDgotTprelL",
                         [(set i64:$rD,
                           (PPCldGotTprelL tglobaltlsaddr:$disp, i64:$reg))]>,
                  isPPC64;
 
-let isBarrier = 1, isPseudo = 1, Defs = [CR7], Itinerary = IIC_LdStSync in
+let isPseudo = 1, Defs = [CR7], Itinerary = IIC_LdStSync in
 def CFENCE8 : Pseudo<(outs), (ins g8rc:$cr), "#CFENCE8", []>;
 
 def : Pat<(PPCaddTls i64:$in, tglobaltlsaddr:$g),
           (ADD8TLS $in, tglobaltlsaddr:$g)>;
 def ADDIStlsgdHA: Pseudo<(outs g8rc:$rD), (ins g8rc_nox0:$reg, s16imm64:$disp),
                          "#ADDIStlsgdHA",
                          [(set i64:$rD,
                            (PPCaddisTlsgdHA i64:$reg, tglobaltlsaddr:$disp))]>,