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.

run-gdbserver

@@ -0,0 +1,26 @@
+#!/usr/bin/env python3
+
+import glob
+import os
+import subprocess
+import sys
+
+import common
+
+parser = common.get_argparse(argparse_args={
+    'description':'Connect to gdbserver running on the guest.'
+})
+parser.add_argument(
+    'executable',
+    help='Path to the executable to be debugged relative to the Buildroot build directory.'
+)
+args = common.setup(parser)
+sys.exit(subprocess.Popen([
+  common.get_toolchain_tool('gdb'),
+  '-q',
+  '-ex', 'set sysroot {}'.format(common.staging_dir),
+  '-ex', 'target remote localhost:{}'.format(common.qemu_hostfwd_generic_port),
+  '-ex', 'tbreak main',
+  '-ex', 'continue',
+  os.path.join(common.build_dir, args.executable),
+]).wait())