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/meadow/main.py

@@ -0,0 +1,95 @@
+import sys
+import os
+import tomli
+from seed import Seed
+from target import Target
+from platform import Platform
+from config import Config
+from cache import Cache
+from command import Command, UserCommand
+from args import Args
+from env import Environment
+from dependency import SeedDependency, DependencyResolutionError
+from builtin import *
+from colorama import init as colorama_init
+from colorama import Fore, Style
+
+
+def main():
+    colorama_init()
+    Command.register(SetCommand())
+    Command.register(SeedsCommand())
+    Command.register(PlatformsCommand())
+    Command.register(HelpCommand())
+    Command.register(BuildCommand())
+    Command.register(CleanCommand())
+    Config.load()
+    Cache.load()
+    Environment.set_source_root(os.getcwd())
+
+    Seed.scan_directory([
+        'base',
+        'external',
+        'interface',
+        'toolchain',
+        'lib',
+        'programs',
+        'services',
+        'sys'
+    ])
+
+    UserCommand.scan_directory([
+        'toolchain'
+    ])
+
+    Target.scan_directory('./target')
+    platforms = Platform.scan_directory('./arch')
+
+    current_platform = Platform.current_platform()
+    if current_platform:
+        current_platform.load_extensions()
+
+    if len(sys.argv) < 2:
+        print(f'{Fore.CYAN}Usage:{Style.RESET_ALL} {sys.argv[0]} <command> [args...]')
+        return -1
+
+    command_name = sys.argv[1]
+    command = Command.get(command_name)
+    if command is None:
+        print(f'{Fore.RED}Err:{Style.RESET_ALL} unknown command "{command_name}"')
+        return -1
+
+    current_target = Target.current_target()
+    seeds = Seed.all_seeds()
+
+    if current_target is not None:
+        system_dep_names = current_target.base_components()
+
+        for s in seeds.values():
+            if s.name() in system_dep_names or not s.should_include_standard_dependencies():
+                continue
+
+            for n in system_dep_names:
+                    s.add_dependency(n, SeedDependency(parent=s.name(), name=n))
+
+        try:
+            current_target.resolve()
+        except DependencyResolutionError as e:
+            print(f'{Fore.RED}Err:{Style.RESET_ALL} {e}')
+            return -1
+
+    args = Args(sys.argv[2:])
+    result = None
+    try:
+        result = command.run(args)
+    except Exception as e:
+        print(f'{Fore.RED}Err:{Style.RESET_ALL} {e}')
+    finally:
+        Cache.save()
+        Config.save()
+
+    return result
+
+
+if __name__ == '__main__':
+    exit(main())