Add an extern "C" block snippet

snippets/c.lua

@@ -45,6 +45,12 @@ local snippets = {
     end, key('guard')),
   }, {}),
 
+  snippet('externc', {
+    text({ '#ifdef __cplusplus', 'extern "C" {', '#endif', '', '' }),
+    insert(0, ''),
+    text({ '', '', '#ifdef __cplusplus', '}', '#endif' }),
+  }),
+
   -- Doxygen
   snippet('p', {
     text('@param'),