SCons: Format buildsystem files with psf/black

Configured for a max line length of 120 characters.

psf/black is very opinionated and purposely doesn't leave much room for
configuration. The output is mostly OK so that should be fine for us,
but some things worth noting:

- Manually wrapped strings will be reflowed, so by using a line length
  of 120 for the sake of preserving readability for our long command
  calls, it also means that some manually wrapped strings are back on
  the same line and should be manually merged again.

- Code generators using string concatenation extensively look awful,
  since black puts each operand on a single line. We need to refactor
  these generators to use more pythonic string formatting, for which
  many options are available (`%`, `format` or f-strings).

- CI checks and a pre-commit hook will be added to ensure that future
  buildsystem changes are well-formatted.

(cherry picked from commit cd4e46ee65)

platform_methods.py

@@ -14,7 +14,6 @@ else:
 
 
 def run_in_subprocess(builder_function):
-
     @functools.wraps(builder_function)
     def wrapper(target, source, env):
 
@@ -23,38 +22,36 @@ def run_in_subprocess(builder_function):
         source = [node.srcnode().abspath for node in source]
 
         # Short circuit on non-Windows platforms, no need to run in subprocess
-        if sys.platform not in ('win32', 'cygwin'):
+        if sys.platform not in ("win32", "cygwin"):
             return builder_function(target, source, env)
 
         # Identify module
         module_name = builder_function.__module__
         function_name = builder_function.__name__
         module_path = sys.modules[module_name].__file__
-        if module_path.endswith('.pyc') or module_path.endswith('.pyo'):
+        if module_path.endswith(".pyc") or module_path.endswith(".pyo"):
             module_path = module_path[:-1]
 
         # Subprocess environment
         subprocess_env = os.environ.copy()
-        subprocess_env['PYTHONPATH'] = os.pathsep.join([os.getcwd()] + sys.path)
+        subprocess_env["PYTHONPATH"] = os.pathsep.join([os.getcwd()] + sys.path)
 
         # Keep only JSON serializable environment items
-        filtered_env = dict(
-            (key, value)
-            for key, value in env.items()
-            if isinstance(value, JSON_SERIALIZABLE_TYPES)
-        )
+        filtered_env = dict((key, value) for key, value in env.items() if isinstance(value, JSON_SERIALIZABLE_TYPES))
 
         # Save parameters
         args = (target, source, filtered_env)
         data = dict(fn=function_name, args=args)
-        json_path = os.path.join(os.environ['TMP'], uuid.uuid4().hex + '.json')
-        with open(json_path, 'wt') as json_file:
+        json_path = os.path.join(os.environ["TMP"], uuid.uuid4().hex + ".json")
+        with open(json_path, "wt") as json_file:
             json.dump(data, json_file, indent=2)
         json_file_size = os.stat(json_path).st_size
 
-        print('Executing builder function in subprocess: '
-              'module_path=%r, parameter_file=%r, parameter_file_size=%r, target=%r, source=%r' % (
-               module_path, json_path, json_file_size, target, source))
+        print(
+            "Executing builder function in subprocess: "
+            "module_path=%r, parameter_file=%r, parameter_file_size=%r, target=%r, source=%r"
+            % (module_path, json_path, json_file_size, target, source)
+        )
         try:
             exit_code = subprocess.call([sys.executable, module_path, json_path], env=subprocess_env)
         finally:
@@ -62,13 +59,15 @@ def run_in_subprocess(builder_function):
                 os.remove(json_path)
             except (OSError, IOError) as e:
                 # Do not fail the entire build if it cannot delete a temporary file
-                print('WARNING: Could not delete temporary file: path=%r; [%s] %s' %
-                      (json_path, e.__class__.__name__, e))
+                print(
+                    "WARNING: Could not delete temporary file: path=%r; [%s] %s" % (json_path, e.__class__.__name__, e)
+                )
 
         # Must succeed
         if exit_code:
             raise RuntimeError(
-                'Failed to run builder function in subprocess: module_path=%r; data=%r' % (module_path, data))
+                "Failed to run builder function in subprocess: module_path=%r; data=%r" % (module_path, data)
+            )
 
     return wrapper
 
@@ -78,5 +77,5 @@ def subprocess_main(namespace):
     with open(sys.argv[1]) as json_file:
         data = json.load(json_file)
 
-    fn = namespace[data['fn']]
-    fn(*data['args'])
+    fn = namespace[data["fn"]]
+    fn(*data["args"])