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-gdb-user

@@ -0,0 +1,35 @@
+#!/usr/bin/env python3
+
+import imp
+import os
+import sys
+
+import common
+rungdb = imp.load_source('rungdb', os.path.join(common.root_dir, 'run-gdb'))
+
+parser = common.get_argparse(argparse_args={
+    'description': '''GDB step debug guest userland processes without gdbserver.
+
+More information at: https://github.com/cirosantilli/linux-kernel-module-cheat#gdb-step-debug-userland-processes
+'''
+})
+parser.add_argument(
+    'executable',
+    help='Path to the executable to be debugged relative to the Buildroot build directory.'
+)
+parser.add_argument(
+    'break',
+    default=None,
+    help='Break at this point, e.g. main.',
+    nargs='?'
+)
+args = common.setup(parser)
+addr = common.get_elf_entry(os.path.join(common.build_dir, args.executable))
+extra_args = {}
+extra_args['before'] = '-ex \"add-symbol-file {} {}\"'.format(args.executable, hex(addr))
+# Or else lx-symbols throws for arm:
+# gdb.MemoryError: Cannot access memory at address 0xbf0040cc
+# TODO understand better.
+# Also, lx-symbols overrides the add-symbol-file commands.
+extra_args['no_lxsymbols'] = True
+sys.exit(rungdb.main(args, extra_args))