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/env.py

@@ -0,0 +1,28 @@
+import os
+
+
+source_root = None
+
+
+class Environment:
+    def set_source_root(path):
+        global source_root
+        source_root = path
+
+
+    def source_root():
+        global source_root
+        return source_root
+
+
+    def build_root():
+        global source_root
+        return os.path.join(source_root, 'build')
+
+
+    def system_root():
+        return os.path.join(Environment.build_root(), 'target-root')
+
+
+    def native_root():
+        return os.path.join(Environment.build_root(), 'host-root')