gem5: support variants

gem5/build

@@ -3,7 +3,7 @@ set -eu
 arch=x86_64
 cross_compile=
 j=
-outdir="$(pwd)/out"
+outdir="$(pwd)"
 while getopts a:c:j:o: OPT; do
   case "$OPT" in
     a)
@@ -28,7 +28,6 @@ system_dir="${outdir}/system"
 binaries_dir="${system_dir}/binaries"
 disks_dir="${system_dir}/disks"
 mkdir -p "$binaries_dir" "$disks_dir"
-cd "gem5"
 if [ "$arch" = x86_64 ]; then
   scons -j "$j" --ignore-style "${outdir}/build/X86/gem5.opt"
   f="${disks_dir}/linux-bigswap2.img"