only set oparity_binary/oparity_unary if explicitely specified

oparity_unary, oparity_binary require opindex to be set, which wasn't
always the case.
Also people seem to expect certain semantics from unops/binops, like
being arithmetic operations. So we shouldn't automatically set
oparity_XXX.

scripts/gen_ir.py

@@ -115,14 +115,6 @@ def format_arity(node):
 		return "oparity_dynamic"
 	if arity == "variable":
 		return "oparity_variable"
-	if arity == 0:
-		return "oparity_zero"
-	if arity == 1:
-		return "oparity_unary"
-	if arity == 2:
-		return "oparity_binary"
-	if arity == 3:
-		return "oparity_trinary"
 	return "oparity_any"
 
 def format_pinned(node):

scripts/ir_spec.py

@@ -14,10 +14,11 @@ class Unop(object):
 	"""Unary nodes have exactly 1 input"""
 	name     = "unop"
 	ins      = [
-		("op",  "operand"),
+		("op", "operand"),
 	]
-	op_index = 0
-	pinned   = "no"
+	op_index       = 0
+	pinned         = "no"
+	arity_override = "oparity_unary"
 
 @abstract
 @op
@@ -25,11 +26,12 @@ class Binop(object):
 	"""Binary nodes have exactly 2 inputs"""
 	name     = "binop"
 	ins      = [
-		( "left",   "first operand" ),
-		( "right", "second operand" ),
+		("left",   "first operand"),
+		("right", "second operand"),
 	]
-	op_index = 0
-	pinned   = "no"
+	op_index       = 0
+	pinned         = "no"
+	arity_override = "oparity_binary"
 
 @op
 class Add(Binop):