Run 3.4 build with frozen string mutation detection

https://gist.github.com/fxn/bf4eed2505c76f4fca03ab48c43adc72

Author: pirj

script/functions.sh

@@ -16,6 +16,11 @@ if is_mri_192_plus; then
   export RUBYOPT="--disable=gem"
 fi
 
+if is_ruby_34_plus; then
+  export RUBYOPT="$RUBYOPT -W:deprecated"
+  export RUBYOPT="$RUBYOPT --enable=frozen-string-literal --debug=frozen-string-literal"
+fi
+
 function clone_repo {
   if [ ! -d $1 ]; then # don't clone if the dir is already there
     if [ -z "$2" ]; then

script/predicate_functions.sh

@@ -111,6 +111,14 @@ function is_ruby_31_plus {
   fi
 }
 
+function is_ruby_34_plus {
+  if ruby -e "exit(RUBY_VERSION.to_f >= 3.4)"; then
+    return 0
+  else
+    return 1
+  fi
+}
+
 function rspec_rails_compatible {
   if is_ruby_25_plus; then
     # TODO remove when RSpec-Rails build is 3.1 safe by default