qapi: introduce QAPISchemaIfCond.cgen()

Instead of building prepocessor conditions from a list of string, use
the result generated from QAPISchemaIfCond.cgen() and hide the
implementation details.

Note: this patch introduces a minor regression, generating a redundant
pair of parenthesis. This is mostly fixed in a later patch in this
series ("qapi: replace if condition list with dict [..]")

Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Message-Id: <20210804083105.97531-5-marcandre.lureau@redhat.com>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
[Commit message tweaked]
Signed-off-by: Markus Armbruster <armbru@redhat.com>

scripts/qapi/schema.py

@@ -19,7 +19,7 @@ import os
 import re
 from typing import Optional
 
-from .common import POINTER_SUFFIX, c_name
+from .common import POINTER_SUFFIX, c_name, cgen_ifcond
 from .error import QAPIError, QAPISemError, QAPISourceError
 from .expr import check_exprs
 from .parser import QAPISchemaParser
@@ -29,6 +29,9 @@ class QAPISchemaIfCond:
     def __init__(self, ifcond=None):
         self.ifcond = ifcond or []
 
+    def cgen(self):
+        return cgen_ifcond(self.ifcond)
+
     def is_present(self):
         return bool(self.ifcond)