Replaced S++ submodule with loader script.

.gitmodules

@@ -1,3 +0,0 @@
-[submodule "scons-plus-plus"]
-	path = external/scons-plus-plus
-	url = https://git.mewin.de/mewin/scons-plus-plus.git

external/scons-plus-plus

@@ -1 +0,0 @@
-Subproject commit 9436d2c48d91dc104099d8805c696a85d7bd37f2

external/scons-plus-plus/SConscript

@@ -0,0 +1,84 @@
+"""
+SCons++ Bootstrapper
+"""
+
+
+import os
+from pathlib import Path
+import shutil
+import subprocess
+import sys
+from SCons.Environment import Environment
+
+
+Import('config')
+
+
+_SPP_FOLDER_NAME = 'scons-plus-plus'
+_SPP_DEFAULT_REPOSITORY = 'https://git.mewin.de/mewin/scons-plus-plus.git'
+_SPP_DEFAULT_BRANCH = 'master'
+
+
+spp_root: Path
+spp_repository: str
+spp_branch: str
+
+def _main() -> Environment:
+    global spp_root, spp_repository, spp_branch
+
+    spp_root = config.get('SPP_ROOT')
+    if spp_root is None:
+        spp_root = _get_default_spp_root()
+    elif not isinstance(spp_root, Path):
+        spp_root = Path(str(spp_root))
+    spp_root = spp_root.absolute()
+
+    spp_repository = config.get('SPP_REPOSITORY', _SPP_DEFAULT_REPOSITORY)
+    spp_branch = config.get('SPP_BRANCH', _SPP_DEFAULT_BRANCH)
+
+    _printinfo(f'Using SCons++ root at: {spp_root}')
+
+    if not spp_root.exists():
+        _printinfo('SCons++ does not yet exist, downloading it.')
+        _install_spp()
+
+    spp_script = spp_root / 'SConscript'
+    if not spp_script.exists():
+        _printerr(f'SCons++ main script not found at {spp_script}!')
+        sys.exit(1)
+    return SConscript(spp_script, exports=['config'])
+
+def _get_default_spp_root() -> Path:
+    if os.name == 'posix':
+        # follow XDG specification -> first try $XDG_DATA_HOME, then $HOME/.local/share
+        data_home = os.environ.get('XDG_DATA_HOME')
+        if data_home is not None:
+            return Path(data_home, _SPP_FOLDER_NAME)
+        home = os.environ.get('HOME')
+        if home is not None:
+            return Path(home, '.local', 'share', _SPP_FOLDER_NAME)
+    elif os.name == 'nt':
+        # just use LocalAppData, which should always be set on Windows
+        return Path(os.environ['LocalAppData'], _SPP_FOLDER_NAME)
+    _printinfo(f'Could not detect SCons++ root directory, falling back to ./{_SPP_FOLDER_NAME}.')
+    return Path(_SPP_FOLDER_NAME)
+
+def _install_spp() -> None:
+    git_exe = shutil.which('git')
+    if git_exe is None:
+        _printerr('No git executable found, cannot install SCons++.')
+        sys.exit(1)
+    _exec_checked((git_exe, 'clone', '-b', spp_branch, '--progress', spp_repository, spp_root))
+
+def _exec_checked(args: Sequence[str], **kwargs) -> None:
+    subprocess.run(args, stdout=sys.stdout, stderr=sys.stderr, check=True, **kwargs)
+
+if not GetOption('silent'):
+    _printinfo = print
+else:
+    def _printinfo(*args): ...
+def _printerr(*args) -> None:
+    print(*args, file=sys.stderr)
+
+env = _main()
+Return('env')