Build the Linux kernel independently from Buildroot

This will allow for other types of root filesystems that don't rely on Buildroot
to be added and used in the future.

Propagate --verbose on all build scripts to see full GCC commands.

build-all: allow for neat subsets

also 9p share rootfs_overlay. TODO document.

run-toolchain

@@ -36,10 +36,15 @@ parser.add_argument(
     nargs='*'
 )
 args = common.setup(parser)
+if args.baremetal is None:
+    image = common.vmlinux
+else:
+    image = common.image
+tool= common.get_toolchain_tool(args.tool, allowed_toolchains=allowed_toolchains)
 if args.dry:
-    print(common.get_toolchain_tool(args.tool))
+    print(tool)
 else:
     sys.exit(common.run_cmd(
-        [common.get_toolchain_tool(args.tool)] + args.extra_args,
+        [tool] + args.extra_args,
         cmd_file=os.path.join(common.run_dir, 'run-toolchain.sh'),
     ))