X86: Conditional tail calls should not have isBarrier = 1

X86: Conditional tail calls should not have isBarrier = 1

That confuses e.g. machine basic block placement, which then doesn't
realize that control can fall through a block that ends with a conditional
tail call. Instead, isBranch=1 should be set.

Also, mark EFLAGS as used by these instructions.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@281281 91177308-0d34-0410-b5e6-96231b3b80d8