alpha: Remove ALPHA tru64 support and associated tests

No one appears to be using it, and it is causing build issues
and increases the development and maintenance effort.

kern, arm: Dump dmesg on kernel panic/oops

Add helper functions to dump the guest kernel's dmesg buffer to a text
file in m5out. This functionality is split into two parts. First, a
dmesg dump function that can be used in other places:

void Linux::dumpDmesg(ThreadContext *, std::ostream &)

This function is used to implement two PCEvents: DmesgDumpEvent and
KernelPanic event. The only difference between the two is that the
latter produces a gem5 panic instead of a warning in addition to
dumping the kernel log.

Change-Id: I6d2af1d666ace57124089648ea906f6c787ac63c
Signed-off-by: Andreas Sandberg <andreas.sandberg@arm.com>
Reviewed-by: Nikos Nikoleris <nikos.nikoleris@arm.com>
Reviewed-by: Gabor Dozsa <gabor.dozsa@arm.com>

arch, base, dev, kern, sym: FreeBSD support

This adds support for FreeBSD/aarch64 FS and SE mode (basic set of syscalls only)

Committed by: Nilay Vaish <nilay@cs.wisc.edu>

kern: get rid of unused linux syscall files

arch: Resurrect the NOISA build target and rename it NULL

This patch makes it possible to once again build gem5 without any
ISA. The main purpose is to enable work around the interconnect and
memory system without having to build any CPU models or device models.

The regress script is updated to include the NULL ISA target. Currently
no regressions make use of it, but all the testers could (and perhaps
should) transition to it.

SE/FS: Get rid of FULL_SYSTEM in kern.

SE/FS: Make the functions available from the TC consistent between SE and FS.

SE/FS: Compile in system events in SE mode.

SE/FS: Build syscall_emul.cc in FS mode.

scons: rename TraceFlags to DebugFlags

SCons: Support building without an ISA

Fix issue 326: glibc non-deterministic because it reads /proc

SCons: centralize the Dir() workaround for newer versions of scons.
Scons bug id: 2006 M5 Bug id: 308

SCons: Fix more SCons version issues

SCons: Fixing SCons bug 2006 issues for non-alpha ISAs

SCons: More scons fixing for SCons bug 2006

Traceflags: Add SCons function to created a traceflag instead of having one file with them all.

Rework the way SCons recurses into subdirectories, making it
automatic. The point is that now a subdirectory can be added
to the build process just by creating a SConscript file in it.
The process has two passes. On the first pass, all subdirs
of the root of the tree are searched for SConsopts files.
These files contain any command line options that ought to be
added for a particular subdirectory. On the second pass,
all subdirs of the src directory are searched for SConscript
files. These files describe how to build any given subdirectory.
I have added a Source() function. Any file (relative to the
directory in which the SConscript resides) passed to that
function is added to the build. Clean up everything to take
advantage of Source().
function is added to the list of files to be built.

Put kernel_stats back into arch.

Made kern a switching header file directory.

SConstruct:
Put the code to make a switching header directory into a function so they are easy to make.
src/arch/SConscript:
Replace switching header code with the new function call.
src/kern/SConscript:
Created a new switching header directory in kern, and moved the declaration of some source files here.