tests: add squashfs make to m5-exit

An ARM squashfs rootfs that runs m5 exit can be generated for example
with:

make ARCH=arm_A64 CROSS_COMPILE=aarch64-linux-gnu- squashfs

The existing Makefile.x86 was not used as a basis because we would
like to provide a setup that allows users to use their own compilers
if they wish, without requiring dockcross.

Change-Id: I19c54cf0575b405f191f45aaf1e4a05c3f2e69ae
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/22223
Reviewed-by: Bobby R. Bruce <bbruce@ucdavis.edu>
Reviewed-by: Andreas Sandberg <andreas.sandberg@arm.com>
Reviewed-by: Jason Lowe-Power <jason@lowepower.com>
Maintainer: Jason Lowe-Power <jason@lowepower.com>
Tested-by: kokoro <noreply+kokoro@google.com>

tests/test-progs/m5-exit/src/.gitignore

@@ -0,0 +1,3 @@
+/m5_exit
+/m5_exit.squashfs
+/squashfs_root

tests/test-progs/m5-exit/src/Makefile

@@ -0,0 +1,59 @@
+# Copyright (c) 2019 ARM Limited
+# All rights reserved.
+#
+# Redistribution and use in source and binary forms, with or without
+# modification, are permitted provided that the following conditions are
+# met: redistributions of source code must retain the above copyright
+# notice, this list of conditions and the following disclaimer;
+# redistributions in binary form must reproduce the above copyright
+# notice, this list of conditions and the following disclaimer in the
+# documentation and/or other materials provided with the distribution;
+# neither the name of the copyright holders nor the names of its
+# contributors may be used to endorse or promote products derived from
+# this software without specific prior written permission.
+#
+# THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+# "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+# LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+# A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+# OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+# SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+# LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+# DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+# THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+# (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+# OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+#
+# Authors: Ciro Santilli
+
+ARCH = x86
+CC = gcc
+CFLAGS = -static -O2
+OUT = $(OUTDIR)/m5_exit
+OUTDIR = ./
+SQUASHFS = $(OUT).squashfs
+SQUASHFS_ROOT = $(OUTDIR)/squashfs_root
+INIT = $(SQUASHFS_ROOT)/sbin/init
+
+.PHONY: all squashfs
+
+all: $(OUT)
+
+$(OUT): m5-exit.c
+	$(CROSS_COMPILE)$(CC) \
+	-DM5 \
+	-I $(CURDIR)/../../../../include/ \
+	-o $@ \
+	$(CFLAGS) \
+	$(CURDIR)/../../../../util/m5/m5op_$(ARCH).S \
+	$<
+
+squashfs: $(SQUASHFS)
+
+$(SQUASHFS): $(OUT)
+	mkdir -p $$(dirname $(INIT))
+	cp $< $(INIT)
+	mksquashfs $(SQUASHFS_ROOT) $(SQUASHFS)
+
+clean:
+	rm -fr $(SQUASHFS) $(SQUASHFS_ROOT) $(OUT)