Add libtool to apt prereqs

- scv (verification extensions for SystemC) requires libtool to build
- Ubuntu 20.04 doesnt have this package installed by default

Change-Id: Iddaa777eb7bedc08e5e6fe9bfb775c0b109aba63

install-prereqs.sh

diff --git a/install-prereqs.sh b/install-prereqs.sh
index 038f7cc..d44c388 100755
--- a/install-prereqs.sh
+++ b/install-prereqs.sh
@@ -42,6 +42,7 @@
     libclang-dev
     libcunit1-dev
     libc6-dev
+    libtool
     llvm-11-tools
     gcc
     g++