qemu: build variants

common

@@ -112,6 +112,12 @@ set_common_vars() {
       ;;
   esac
   common_linux_image="${common_linux_variant_dir}/${common_linux_image}"
+  if "$common_prebuilt"; then
+    common_mkdir
+    common_qemu_executable="qemu-system-${arch}"
+  else
+    common_qemu_executable="${common_qemu_variant_dir}/${arch}-softmmu/qemu-system-${arch}"
+  fi
 
   # Ports.
   common_run_id_number="$(echo "$common_run_id" | cut -d . -f 2)"
@@ -150,6 +156,7 @@ common_gem5_default_src_dir="${root_dir}/gem5/gem5"
 common_gem5_non_default_src_root_dir="${data_dir}/gem5"
 common_gem5_worktree=
 common_gem5_variant=default
+common_prebuilt=false
 common_run_id=0
 f="${data_dir}/cli"
 if [ -f "$f" ]; then