run_tests.py: use mlog.log_once to avoid spamming ninja < 1.9 warnings

run_tests.py

@@ -211,7 +211,7 @@ def get_backend_commands(backend, debug=False):
                 if v == '1.9':
                     NINJA_1_9_OR_NEWER = True
                 else:
-                    print('Found ninja <1.9, tests will run slower')
+                    mlog.warning('Found ninja <1.9, tests will run slower', once=True)
                     if 'CI' in os.environ:
                         raise RuntimeError('Require ninja >= 1.9 when running on Meson CI')
                 break
@@ -238,12 +238,12 @@ def ensure_backend_detects_changes(backend):
     # XXX: Upgrade Travis image to Apple FS when that becomes available
     # TODO: Detect HFS+ vs APFS
     if mesonlib.is_osx():
-        print('Running on HFS+, enabling timestamp resolution workaround')
+        mlog.warning('Running on HFS+, enabling timestamp resolution workaround', once=True)
         need_workaround = True
     # We're using ninja >= 1.9 which has QuLogic's patch for sub-1s resolution
     # timestamps
     if not NINJA_1_9_OR_NEWER:
-        print('Don\'t have ninja >= 1.9, enabling timestamp resolution workaround')
+        mlog.warning('Don\'t have ninja >= 1.9, enabling timestamp resolution workaround', once=True)
         need_workaround = True
     # Increase the difference between build.ninja's timestamp and the timestamp
     # of whatever you changed: https://github.com/ninja-build/ninja/issues/371