audit: check for build_universal? calls if --universal unused

Closes Homebrew/homebrew#8123.

Signed-off-by: Jack Nagel <jacknagel@gmail.com>

Library/Homebrew/cmd/audit.rb

@@ -151,7 +151,7 @@ def audit_formula_options f, text
 
   if documented_options.length > 0
     documented_options.each do |o|
-      next if o == '--universal'
+      next if o == '--universal' and text =~ /ARGV\.build_universal\?/
       problems << " * Option #{o} is unused" unless options.include? o
     end
   end