mlog: make mlog helper take once keyword argument

We really want to have this in the log method as well.

Fixes: mesonbuild#8002

mesonbuild/mlog.py

@@ -218,7 +218,15 @@ def _debug_log_cmd(cmd: str, args: T.List[str]) -> None:
 def cmd_ci_include(file: str) -> None:
     _debug_log_cmd('ci_include', [file])
 
+
 def log(*args: T.Union[str, AnsiDecorator], is_error: bool = False,
+        once: bool = False, **kwargs: T.Any) -> None:
+    if once:
+        return log_once(*args, is_error=is_error, **kwargs)
+    return _log(*args, is_error=is_error, **kwargs)
+
+
+def _log(*args: T.Union[str, AnsiDecorator], is_error: bool = False,
         **kwargs: T.Any) -> None:
     arr = process_markup(args, False)
     if log_file is not None:
@@ -240,7 +248,7 @@ def log_once(*args: T.Union[str, AnsiDecorator], is_error: bool = False,
     if t in _logged_once:
         return
     _logged_once.add(t)
-    log(*args, is_error=is_error, **kwargs)
+    _log(*args, is_error=is_error, **kwargs)
 
 # This isn't strictly correct. What we really want here is something like:
 # class StringProtocol(typing_extensions.Protocol):
@@ -280,10 +288,7 @@ def _log_error(severity: str, *rargs: T.Union[str, AnsiDecorator],
         location_list = T.cast(T.List[T.Union[str, AnsiDecorator]], [location_str])
         args = location_list + args
 
-    if once:
-        log_once(*args, **kwargs)
-    else:
-        log(*args, **kwargs)
+    log(*args, once=once, **kwargs)
 
     global log_warnings_counter
     log_warnings_counter += 1