qapi: make 'if' condition strings simple identifiers

Change the 'if' condition strings to be C-agnostic. It will accept
'[A-Z][A-Z0-9_]*' identifiers. This allows to express configuration
conditions in other languages (Rust or Python for ex) or other more
suitable forms.

Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Tested-by: John Snow <jsnow@redhat.com>
Message-Id: <20210804083105.97531-11-marcandre.lureau@redhat.com>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
[Rebased with semantic conflict in redefined-event.json]
Signed-off-by: Markus Armbruster <armbru@redhat.com>
diff --git a/qapi/sockets.json b/qapi/sockets.json
index 735eb4a..7866dc2 100644
--- a/qapi/sockets.json
+++ b/qapi/sockets.json
@@ -69,7 +69,7 @@
     '*ipv4': 'bool',
     '*ipv6': 'bool',
     '*keep-alive': 'bool',
-    '*mptcp': { 'type': 'bool', 'if': 'defined(IPPROTO_MPTCP)' } } }
+    '*mptcp': { 'type': 'bool', 'if': 'IPPROTO_MPTCP' } } }
 
 ##
 # @UnixSocketAddress:
@@ -89,8 +89,8 @@
 { 'struct': 'UnixSocketAddress',
   'data': {
     'path': 'str',
-    '*abstract': { 'type': 'bool', 'if': 'defined(CONFIG_LINUX)' },
-    '*tight': { 'type': 'bool', 'if': 'defined(CONFIG_LINUX)' } } }
+    '*abstract': { 'type': 'bool', 'if': 'CONFIG_LINUX' },
+    '*tight': { 'type': 'bool', 'if': 'CONFIG_LINUX' } } }
 
 ##
 # @VsockSocketAddress: