gem5: update to 7bfb7f3a43f382eb49853f47b140bfd6caad0fb8

The update is required to include 3c3ca64b5f0dd9eef7b1ce1c65cc6e8e9147dd38
otherwise baremetal does not on VExpress.

baremetal: create a baremetal setup with crosstool-ng

buildroot: improve directory location: move out/dl inside
out/buildroot/download, and add a new out/buildroot/build level

tagline: generalize, deliver more value than howto, since now howtos
are starting to multiply

rename all top scripts to separate words with hyphen more consistently,
e.g. run-gdb instead of rungdb

getvar: list all variables

gem5: make m5out section to focus all releated information at

Prevent m5term Text file busy when rebuilding gem5 while it is running.

build-crosstool-ng

@@ -0,0 +1,83 @@
+#!/usr/bin/env python3
+
+import multiprocessing
+import os
+import shutil
+import sys
+import time
+
+import common
+
+def get_argparse():
+    parser = common.get_argparse(argparse_args={
+        'description': 'Build crosstool-NG with Newlib for bare metal compilation'
+    })
+    common.add_build_arguments(parser)
+    return parser
+
+def main(args, extra_args=None):
+    common.raise_no_x86(args.arch)
+    nproc = multiprocessing.cpu_count()
+    defconfig_dest = os.path.join(common.crosstool_ng_util_dir, 'defconfig')
+    os.makedirs(common.crosstool_ng_util_dir, exist_ok=True)
+    os.makedirs(common.crosstool_ng_download_dir, exist_ok=True)
+
+    # Bootstrap out-ot-tree WONTFIX. I've tried.
+    # https://github.com/crosstool-ng/crosstool-ng/issues/1021
+    os.chdir(common.crosstool_ng_src_dir)
+    assert common.run_cmd(
+        [os.path.join(common.crosstool_ng_src_dir, 'bootstrap')],
+    ) == 0
+    os.chdir(common.crosstool_ng_util_dir)
+    assert common.run_cmd(
+        [
+            os.path.join(common.crosstool_ng_src_dir, 'configure'),
+            '--enable-local',
+        ],
+    ) == 0
+    assert common.run_cmd(
+        [
+            'make',
+            '-j', str(nproc)
+        ],
+    ) == 0
+
+    # Build the toolchain.
+    shutil.copy2(
+        os.path.join(common.root_dir, 'crosstool_ng_config', args.arch),
+        defconfig_dest
+    )
+    common.write_configs(
+        common.crosstool_ng_defconfig,
+        [
+            'CT_PREFIX_DIR="{}"'.format(common.crosstool_ng_install_dir),
+            'CT_WORK_DIR="{}"'.format(common.crosstool_ng_build_dir),
+            'CT_LOCAL_TARBALLS_DIR="{}"'.format(common.crosstool_ng_download_dir),
+        ]
+    )
+    assert common.run_cmd(
+        [
+            common.crosstool_ng_executable,
+            'defconfig',
+        ],
+    ) == 0
+    os.unlink(defconfig_dest)
+    assert common.run_cmd(
+        [
+            common.crosstool_ng_executable,
+            'build',
+            '-j', str(nproc)
+        ],
+        out_file=os.path.join(common.crosstool_ng_build_dir, 'lkmc.log'),
+        delete_env=['LD_LIBRARY_PATH'],
+        extra_env={'PATH': common.ccache_dir + ':' + os.environ['PATH']},
+    ) == 0
+
+if __name__ == '__main__':
+    parser = get_argparse()
+    args = common.setup(parser)
+    start_time = time.time()
+    exit_status = main(args)
+    end_time = time.time()
+    common.print_time(end_time - start_time)
+    sys.exit(exit_status)