Update gclient_gn_args_file to a relative path.

This is necessary, now that gclient interprets gclient_gn_args_file
differently when |use_relative_paths| is set to True.

Bug: chromium:1102833
Change-Id: I62e87b0aaaa99fefbb4b2fb204087f0f90f9d106
Reviewed-on: https://pdfium-review.googlesource.com/c/pdfium/+/71491
Reviewed-by: Daniel Hosseinian <dhoss@chromium.org>
Commit-Queue: Lei Zhang <thestig@chromium.org>

DEPS

diff --git a/DEPS b/DEPS
index 73c64c7..cea494b 100644
--- a/DEPS
+++ b/DEPS
@@ -1,7 +1,7 @@
 use_relative_paths = True
 use_relative_hooks = True
 
-gclient_gn_args_file = 'pdfium/build/config/gclient_args.gni'
+gclient_gn_args_file = 'build/config/gclient_args.gni'
 gclient_gn_args = [
   'checkout_google_benchmark',
   'mac_xcode_version',