regrtest: add -u for unbuffered stdout/stderr

Lib/test/libregrtest/runtest_mp.py

@@ -41,7 +41,7 @@ def run_test_in_subprocess(testname, ns):
     slaveargs = json.dumps(slaveargs)
 
     cmd = [sys.executable, *support.args_from_interpreter_flags(),
-           '-X', 'faulthandler',
+           '-u',    # Unbuffered stdout and stderr
            '-m', 'test.regrtest',
            '--slaveargs', slaveargs]
     if ns.pgo:

PCbuild/rt.bat

@@ -42,7 +42,7 @@ if "%1"=="-x64" (set prefix=%pcbuild%amd64\) & shift & goto CheckOpts
 if NOT "%1"=="" (set regrtestargs=%regrtestargs% %1) & shift & goto CheckOpts
 
 set exe=%prefix%python%suffix%.exe
-set cmd="%exe%" %dashO% -Wd -E -bb -m test %regrtestargs%
+set cmd="%exe%" %dashO% -u -Wd -E -bb -m test %regrtestargs%
 if defined qmode goto Qmode
 
 echo Deleting .pyc/.pyo files ...

Tools/scripts/run_tests.py

@@ -26,6 +26,7 @@ def is_resource_use_flag(arg):
 
 def main(regrtest_args):
     args = [sys.executable,
+            '-u',                 # Unbuffered stdout and stderr
             '-W', 'default',      # Warnings set to 'default'
             '-bb',                # Warnings about bytes/bytearray
             '-E',                 # Ignore environment variables