Add missing import statement for gyp-patches.nix.

--- a/deps/npm/node_modules/node-gyp/gyp/pylib/gyp/generator/make.py
+++ b/deps/npm/node_modules/node-gyp/gyp/pylib/gyp/generator/make.py
@@ -25,6 +25,7 @@
 import os
 import re
 import subprocess
+import sys
 import gyp
 import gyp.common
 import gyp.xcode_emulation

--- a/tools/gyp/pylib/gyp/generator/make.py
+++ b/tools/gyp/pylib/gyp/generator/make.py
@@ -25,6 +25,7 @@
 import os
 import re
 import subprocess
+import sys
 import gyp
 import gyp.common
 import gyp.xcode_emulation