[build] Move to python build scripts per module

This change moves Bonnibel from a separate project into the jsix tree,
and alters the project configuration to be jsix-specific. (I stopped
using bonnibel for any other projects, so it's far easier to make it a
custom generator for jsix.) The build system now also uses actual python
code in `*.module` files to configure modules instead of TOML files.
Target configs (boot, kernel-mode, user-mode) now moved to separate TOML
files under `configs/` and can inherit from one another.

scripts/bonnibel/target.py

@@ -0,0 +1,50 @@
+class Target(dict):
+    __targets = {}
+
+    @classmethod
+    def load(cls, root, name, config=None):
+        import toml
+
+        if (name, config) in cls.__targets:
+            return cls.__targets[(name, config)]
+
+        configs = root / "configs"
+
+        dicts = []
+        depfiles = []
+        basename = name
+        if config:
+            basename += f"-{config}"
+
+        while basename is not None:
+            filename = str(configs / (basename + ".toml"))
+            depfiles.append(filename)
+            desc = toml.load(filename)
+            basename = desc.get("extends")
+            dicts.append(desc.get("variables", dict()))
+
+        t = Target(name, config, depfiles)
+        for d in reversed(dicts):
+            for k, v in d.items():
+                if isinstance(v, (list, tuple)):
+                    t[k] = t.get(k, list()) + list(v)
+                elif isinstance(v, dict):
+                    t[k] = t.get(k, dict())
+                    t[k].update(v)
+                else:
+                    t[k] = v
+
+        cls.__targets[(name, config)] = t
+        return t
+
+    def __init__(self, name, config, depfiles):
+        self.__name = name
+        self.__config = config
+        self.__depfiles = tuple(depfiles)
+
+    def __hash__(self):
+        return hash((self.__name, self.__config))
+
+    name = property(lambda self: self.__name)
+    config = property(lambda self: self.__config)
+    depfiles = property(lambda self: self.__depfiles)