[Verifier] add missing checks for convergence control intrinsics

; RUN: not llvm-as < %s -o /dev/null 2>&1 | FileCheck %s

; CHECK: Entry or anchor intrinsic must not have a convergencectrl bundle.

; CHECK-NEXT: %t04_tok2 = call token

; CHECK: Loop intrinsic must have a convergencectrl bundle.

; CHECK-NEXT: %t04_tok3 = call token

define void @basic_syntax() {

  %t04_tok1 = call token @llvm.experimental.convergence.anchor()

  %t04_tok2 = call token @llvm.experimental.convergence.anchor() [ "convergencectrl"(token %t04_tok1) ]

  %t04_tok3 = call token @llvm.experimental.convergence.loop()

  ret void

}

; CHECK: Convergence control tokens can only be produced by calls to the convergence control intrinsics.

; CHECK-NEXT:  %t04_tok1 = call token @produce_token()

; CHECK-NEXT:  call void @f() [ "convergencectrl"(token %t04_tok1) ]