gcc: enable syntax highlighting

lib/docs/filters/gcc/clean_html.rb

@@ -0,0 +1,12 @@
+module Docs
+  class Gcc
+    class CleanHtmlFilter < Filter
+      def call
+        css('pre').each do |node|
+          node['data-language'] = 'cpp'
+        end
+        doc
+      end
+    end
+  end
+end

lib/docs/scrapers/gnu/gcc.rb

@@ -6,7 +6,7 @@ module Docs
       home: 'https://gcc.gnu.org/'
     }
 
-    html_filters.push 'title'
+    html_filters.push 'gcc/clean_html', 'title'
 
     options[:root_title] = false
     options[:title] = false