Convert the Branch and Jump instruction formats to value_list.

The Branch format also stores its fixed argument in the value list. This
requires the value pool to be passed to a few more functions.

Note that this actually makes the Branch and Jump variants of
InstructionData identical. The instruction format hashing does not yet
understand that all value operands are stored in the value list. We'll
fix that in a later patch.

Also convert IndirectCall, noting that Call and IndirectCall remain
separate instruction formats because they have different immediate
fields.

lib/cretonne/meta/gen_instr.py

@@ -206,12 +206,19 @@ def gen_instruction_data_impl(fmt):
 
         fmt.doc_comment('Get the controlling type variable operand.')
         with fmt.indented(
-                'pub fn typevar_operand(&self) -> Option<Value> {', '}'):
+                'pub fn typevar_operand(&self, pool: &ValueListPool) -> '
+                'Option<Value> {', '}'):
             with fmt.indented('match *self {', '}'):
                 for f in InstructionFormat.all_formats:
                     n = 'InstructionData::' + f.name
                     if f.typevar_operand is None:
                         fmt.line(n + ' { .. } => None,')
+                    elif f.has_value_list:
+                        # We keep all arguments in a value list.
+                        i = f.value_operands.index(f.typevar_operand)
+                        fmt.line(
+                                '{} {{ ref args, .. }} => '
+                                'args.get({}, pool),'.format(n, i))
                     elif len(f.value_operands) == 1:
                         # We have a single value operand called 'arg'.
                         if f.boxed_storage: