Build .less file when relevant .overrides or .variables file is modified

src/Gruntfile.js

@@ -64,6 +64,13 @@ module.exports = function(grunt) {
       if(process.platform === 'win32') {
         filePath = filePath.replace(/\\/g, '/');
       }
+      var
+        re = new RegExp(paths.source.themes + '.*\/([^\/]*\/[^\/]*)\.(?:overrides|variables)$')
+      ;
+      // find relevant .less file for each modified .overrides or .variables file
+      if(filePath.search(re) !== -1) {
+        filePath = filePath.replace(re, paths.source.definitions + '$1.less');
+      }
       var
         outputPath = filePath.replace(paths.source.definitions, paths.output.uncompressed + 'definitions/')
       ;