[build-script] Flush immediately after print() in Python

utils/SwiftBuildSupport.py

@@ -67,6 +67,7 @@ SWIFT_BUILD_ROOT = os.environ.get(
 
 def print_with_argv0(message):
     print(sys.argv[0] + ": " + message)
+    sys.stdout.flush()
 
 
 def quote_shell_command(args):
@@ -82,6 +83,7 @@ def check_call(args, print_command=False, verbose=False, disable_sleep=False):
 
     if print_command:
         print(os.getcwd() + "$ " + quote_shell_command(args))
+        sys.stdout.flush()
     try:
         return subprocess.check_call(args)
     except subprocess.CalledProcessError as e:
@@ -101,6 +103,7 @@ def check_call(args, print_command=False, verbose=False, disable_sleep=False):
 def check_output(args, print_command=False, verbose=False):
     if print_command:
         print(os.getcwd() + "$ " + quote_shell_command(args))
+        sys.stdout.flush()
     try:
         return subprocess.check_output(args)
     except subprocess.CalledProcessError as e:

utils/swift_build_support/swift_build_support/debug.py

@@ -37,5 +37,6 @@ def print_xcodebuild_versions(file=sys.stdout):
     print(u'--- SDK versions ---', file=file)
     print(u'{}\n'.format(_output(['xcodebuild', '-version', '-sdk'])),
           file=file)
+    file.flush()
     # You can't test beyond this because each developer's machines may have
     # a different set of SDKs installed.

utils/swift_build_support/swift_build_support/shell.py

@@ -41,10 +41,11 @@ def _print_command(dry_run, command, env=None, prompt="+ "):
     if env is not None:
         output += ['env'] + [_quote("%s=%s" % (k, v)) for k, v in env]
     output += [_quote(arg) for arg in command]
-    file = None
-    if not dry_run:
     file = sys.stderr
+    if dry_run:
+        file = sys.stdout
     print(prompt + ' '.join(output), file=file)
+    file.flush()
 
 
 def call(command, stderr=None, env=None, dry_run=None):