Fetch architecture-specific GN binary on Linux

Cherry-pick https://crrev.com/1004763

Change-Id: I2f6108b6564108e1517de70fa998f2c65f98bdcb
Reviewed-on: https://pdfium-review.googlesource.com/c/pdfium/+/129374
Reviewed-by: Tom Sepez <tsepez@chromium.org>
Reviewed-by: Thomas Sepez <tsepez@google.com>
Commit-Queue: Lei Zhang <thestig@chromium.org>
diff --git a/DEPS b/DEPS
index d9c47f0..548ed64 100644
--- a/DEPS
+++ b/DEPS
@@ -263,7 +263,7 @@
   'buildtools/linux64': {
     'packages': [
       {
-        'package': 'gn/gn/linux-amd64',
+        'package': 'gn/gn/linux-${{arch}}',
         'version': Var('gn_version'),
       }
     ],