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.

external/magenta-tools.seed

@@ -0,0 +1,15 @@
+[seed]
+name = 'magenta-tools'
+
+[dependency]
+no_standard_dependencies = true
+
+[build]
+build_for = 'host'
+build_system = 'cmake'
+source_dir = 'kernel/tools'
+
+[publish]
+path = [ 'install:bin/' ]
+
+# vim: ft=toml