Add a .gyp suffix to generated makefile, avoid clobbering an existing one.

lib/configure.js

@@ -45,6 +45,8 @@ function configure (gyp, argv, callback) {
       argv.push(path.join(devDir, 'tools', 'patch.gypi'))
     } else {
       // Force the 'make' target for non-Windows
+      argv.unshift('.gyp')
+      argv.unshift('--suffix')
       argv.unshift('make')
       argv.unshift('-f')
     }