fix(gyp): default enable_thin_lto so Node 26 win32 configure works

binding.gyp

@@ -1,4 +1,13 @@
 {
+  # Node 26's common.gypi references variables like `enable_thin_lto` in
+  # `conditions`, but the bundled node-gyp (10.x) shipped with prebuild
+  # 13 doesn't inject defaults for them. On the Windows toolchain that
+  # results in `gyp: name 'enable_thin_lto' is not defined`. Providing a
+  # `%` default here is safe across all platforms and node-gyp versions:
+  # gyp only uses our default when the variable isn't already set.
+  'variables': {
+    'enable_thin_lto%': 'false',
+  },
   'targets': [
     {
       'target_name': 'node_expat',

deps/libexpat/libexpat.gyp

@@ -7,6 +7,12 @@
 #   ./out/Debug/test
 
 {
+  # Same Node 26 / node-gyp 10 workaround as in ../../binding.gyp. gyp loads
+  # dependency .gyp files in their own variable scope, so the default has to
+  # live here too — the parent binding.gyp's variables don't propagate down.
+  'variables': {
+    'enable_thin_lto%': 'false',
+  },
   'target_defaults': {
     'default_configuration': 'Debug',
     'configurations': {