Use a remark, rather than a disembodied note, for constant evaluator

Author: DougGregor

include/swift/AST/DiagnosticsSIL.def

@@ -445,7 +445,7 @@ NOTE(constexpr_witness_call_with_no_conformance, none,
     "%select{for this call|for a witness-method invoked during this call}0",
     (bool))
 
-NOTE(constexpr_unknown_control_flow_due_to_skip,none, "branch depends on "
+REMARK(constexpr_unknown_control_flow_due_to_skip,none, "branch depends on "
      "non-constant value produced by an unevaluated instructions", ())
 NOTE(constexpr_returned_by_unevaluated_instruction,none,
      "result of an unevaluated instruction is not a constant", ())

test/SILOptimizer/constant_evaluator_skip_test.sil

@@ -92,7 +92,7 @@ bb0:
   %9 = integer_literal $Builtin.Int32, 0
   %10 = builtin "cmp_slt_Int32"(%8 : $Builtin.Int32, %9 : $Builtin.Int32) : $Builtin.Int1
   cond_br %10, bb2, bb3
-    // CHECK: {{.*}}:[[@LINE-1]]:{{.*}}: note: branch depends on non-constant value produced by an unevaluated instructions
+    // CHECK-LABEL: {{.*}}:94:{{.*}}: remark: branch depends on non-constant value produced by an unevaluated instructions
     // CHECK: {{.*}}: note: result of an unevaluated instruction is not a constant
 bb2:
   br bb4