configure: make qemu and gem5 steps optional

configure

@@ -1,10 +1,18 @@
 #!/usr/bin/env bash
 set -e
 interactive_pkgs=libsdl2-dev
-submodules='buildroot linux qemu gem5/gem5'
+gem5=false
+qemu=true
+submodules='buildroot linux'
 y=''
-while getopts pt OPT; do
+while getopts gqpt OPT; do
   case "$OPT" in
+    g)
+      gem5=true
+      ;;
+    q)
+      qemu=false
+      ;;
     p)
       submodules="$submodules parsec-benchmark/parsec-benchmark"
       ;;
@@ -16,6 +24,14 @@ while getopts pt OPT; do
 done
 shift $(($OPTIND - 1))
 
+## Submodules
+
+if "$qemu"; then
+  submodules="$submodules qemu"
+fi
+if "$gem5"; then
+  submodules="$submodules gem5/gem5"
+fi
 (
   set -e
   # Shallow cloning saves a considerable amount of time, specially because of the linux kernel.
@@ -25,36 +41,39 @@ shift $(($OPTIND - 1))
   # - `shallow = true` on the submodule has no effect for the non default educational branches of our submodules
   # - QEMU's submodules point to commits that are neither under branches nor tags, and so `--shallow-submodules` fails
   git submodule update --depth 1 --jobs 4 --init -- $submodules
-  cd qemu
-  git submodule update --init
+  if "$qemu"; then
+    cd qemu
+    git submodule update --init
+  fi
 ) &
 wait $! || git submodule update --init -- $submodules
 
+## apt-get
+
 pkgs="\
 automake \
 build-essential \
 coreutils \
 "
-
-# GEM5
-pkgs="$pkgs \
-g++-6 \
-gcc-6 \
-gcc-aarch64-linux-gnu \
-gcc-arm-linux-gnueabi \
-libgoogle-perftools-dev \
-protobuf-compiler \
-"
-
+if "$gem5"; then
+  pkgs="$pkgs \
+  g++-6 \
+  gcc-6 \
+  gcc-aarch64-linux-gnu \
+  gcc-arm-linux-gnueabi \
+  libgoogle-perftools-dev \
+  protobuf-compiler \
+  "
+fi
 command -v apt-get >/dev/null 2>&1 || {
-    cat <<EOF
+  cat <<EOF
 apt-get not found. You're on your own for installing dependencies.
 
 On Ubuntu they are:
 
 $pkgs
 EOF
-    exit 0
+  exit 0
 }
 
 # Without this started failing in kernel 4.15 with:
@@ -71,4 +90,6 @@ sudo apt-get install $y \
   $pkgs \
   $interactive_pkgs \
 ;
-sudo apt-get build-dep $y qemu
+if "$qemu"; then
+  sudo apt-get build-dep $y qemu
+fi