get rid of lkmc package, move userland and kernel-modules to top

Rationale: we already had a non buildroot build system,
maintaining both will be hard, and having short paths is more awesome.

build-overlay

@@ -0,0 +1,73 @@
+
+#!/usr/bin/env python3
+
+import os
+import platform
+import shutil
+import subprocess
+
+import common
+
+class UserlandComponent(common.Component):
+    def add_parser_arguments(self, parser):
+        parser.add_argument(
+            '--has-package',
+            action='append',
+            default=[],
+            help='''\
+Indicate that a given package is present in the root filesystem, which
+allows us to build examples that rely on it.
+''',
+        )
+        parser.add_argument(
+            'targets',
+            default=[],
+            help='''\
+Build only the given userland programs.
+Default: build all examples that have their package dependencies met.
+For example, an OpenBLAS example can only be built if the target root filesystem
+has the OpenBLAS libraries and headers installed.
+''',
+            metavar='programs',
+            nargs='*',
+        )
+
+    def do_build(self, args):
+        build_dir = self.get_build_dir(args)
+        os.makedirs(build_dir, exist_ok=True)
+        allowed_toolchains = ['buildroot']
+        cc = common.get_toolchain_tool('gcc', allowed_toolchains=allowed_toolchains)
+        cxx = common.get_toolchain_tool('g++', allowed_toolchains=allowed_toolchains)
+        common.run_cmd(
+            (
+                [
+                    'make',
+                    '-j', str(args.nproc),
+                    'CC={}'.format(cc),
+                    'CXX={}'.format(cxx),
+                    'PKG_CONFIG={}'.format(common.buildroot_pkg_config),
+                    'STAGING_DIR={}'.format(common.buildroot_staging_dir),
+                    'OUT_DIR={}'.format(build_dir),
+                ] +
+                ['HAS_{}=y'.format(package.upper()) for package in args.has_package] +
+                [os.path.join(build_dir, os.path.splitext(os.path.split(target)[1])[0]) + common.executable_ext for target in args.targets]
+            ),
+            cwd=common.userland_src_dir,
+            extra_paths=[common.ccache_dir],
+        )
+        common.copy_dir_if_update_non_recursive(
+            srcdir=build_dir,
+            destdir=common.out_rootfs_overlay_dir,
+            filter_ext=common.executable_ext,
+        )
+
+    def get_argparse_args(self):
+        return {
+            'description': 'Build our compiled userland examples',
+        }
+
+    def get_build_dir(self, args):
+        return common.userland_build_dir
+
+if __name__ == '__main__':
+    UserlandComponent().build()