Shallow clone to save clone time and disk space

configure

@@ -1,4 +1,5 @@
 #!/usr/bin/env bash
+set -ex
 y=''
 while getopts t OPT; do
   case "$OPT" in
@@ -8,6 +9,9 @@ while getopts t OPT; do
   esac
 done
 shift $(($OPTIND - 1))
+git submodule update --depth 1 --jobs 4 --init
+cd qemu
+git submodule update --init
 sudo apt-get update $y
 # Building SDL for QEMU in Buildroot was rejected upstream because it adds many dependencies:
 # https://patchwork.ozlabs.org/patch/770684/