Specify gcc/g++ 11

It is used to build OT host binaries as well as verilator

Change-Id: I0576ce8544c6f194df71d9655ad1f30a21a68d18

install-prereqs.sh

diff --git a/install-prereqs.sh b/install-prereqs.sh
index 7c02527..858d98e 100755
--- a/install-prereqs.sh
+++ b/install-prereqs.sh
@@ -48,8 +48,8 @@
     llvm-11-tools
     gcc
     g++
-    gcc-10
-    g++-10
+    gcc-11
+    g++-11
     libftdi1
     libftdi1-dev
     libfl2