Backed out changeset ca3dddda32b0 (bug 1361912)

testing/mozharness/mozharness/mozilla/building/buildbase.py

@@ -1636,8 +1636,16 @@ or run without that action (ie: --no-{action})"
                 buildprops,
                 os.path.join(dirs['abs_work_dir'], 'buildprops.json'))
 
+        if 'MOZILLABUILD' in os.environ:
+            mach = [
+                os.path.join(os.environ['MOZILLABUILD'], 'msys', 'bin', 'bash.exe'),
+                os.path.join(dirs['abs_src_dir'], 'mach')
+            ]
+        else:
+            mach = [sys.executable, 'mach']
+
         return_code = self.run_command_m(
-            command=[sys.executable, 'mach', '--log-no-times', 'build', '-v'],
+            command=mach + ['--log-no-times', 'build', '-v'],
             cwd=dirs['abs_src_dir'],
             env=env,
             output_timeout=self.config.get('max_build_output_timeout', 60 * 40)