Bump llvm-11-tools package to llvm-13-tools

The debian testing repositories no longer have llvm-11-tools package.

Change-Id: Iea24b489caa18efad027862640e49eea68a1267a

install-prereqs.sh

diff --git a/install-prereqs.sh b/install-prereqs.sh
index 68d5ec0..7e73251 100755
--- a/install-prereqs.sh
+++ b/install-prereqs.sh
@@ -45,7 +45,7 @@
     libcunit1-dev
     libc6-dev
     libtool
-    llvm-11-tools
+    llvm-13-tools
     gcc
     g++
     gcc-11