meta: replace cmake mono-build system with a custom build co-ordinator

every system component now has its own self-contained build system, and a
seed file describing the component and its build system and dependencies.

a new tool, meadow, collects and uses these seed files to build the
components into a full system. meadow also manages the target system root
and a host prefix where toolchain tools are installed to.

the build system has also been updated to use a new $ARCH-rosetta-gcc
compiler, and the patches files necessary to build it have been
added to toolchain/cross-compiler.

toolchain/mkbsp/preset.py

@@ -0,0 +1,66 @@
+import os
+import sys
+import json
+import tomli
+
+
+class PresetParseError(Exception):
+    pass
+
+
+class Preset:
+    def __collect_preset_files(self):
+        result = []
+        for root, dirs, files in os.walk(self.__path):
+            for f in files:
+                name = f
+                path = os.path.join(root, f)
+
+                result.append((name, path))
+
+        return result
+
+
+    def __apply_preset_file(self, data):
+        bootstrap = data.get('bootstrap', None)
+        contents = data.get('contents', None)
+        if bootstrap is not None:
+            self.__bootstrap = bootstrap
+
+        if contents is not None:
+            for dest, src in contents.items():
+                dest_list = self.__contents.get(dest, [])
+
+                for p in src:
+                    dest_list.append(p)
+
+                self.__contents[dest] = dest_list
+
+
+    def __read_preset_files(self):
+        for n, p in self.__files:
+            data = None
+            try:
+                f = open(p, mode='rb')
+                data = tomli.load(f)
+            except Exception as e:
+                raise ParseError('Err: Failed to parse seed file {}: {}'.format(seed_path, e))
+
+            self.__apply_preset_file(data)
+
+
+    def __init__(self, path):
+        self.__bootstrap = {}
+        self.__contents = {}
+        self.__path = path
+        self.__files = self.__collect_preset_files()
+        self.__files = sorted(self.__files, key=lambda tup: tup[0])
+        self.__read_preset_files()
+
+
+    def contents(self):
+        return self.__contents
+
+
+    def bootstrap_program(self):
+        return self.__bootstrap.get('bootstrap_exec', None)