Fix non-standalone XFA build.

The new GN build target for fxjs/gc from
https://pdfium-review.googlesource.com/73434 is missing a configs
variable. As a result, there's no include path to point to fxjs/gc in
non-standalone builds, as seen with https://crrev.com/c/2402638

Tbr: tsepez@chromium.org
Bug: pdfium:1563
Change-Id: I5ed5f6c36c062d380aa19bca2efab0ede4d7faed
Reviewed-on: https://pdfium-review.googlesource.com/c/pdfium/+/73436
Reviewed-by: Lei Zhang <thestig@chromium.org>
Commit-Queue: Lei Zhang <thestig@chromium.org>
diff --git a/fxjs/BUILD.gn b/fxjs/BUILD.gn
index 1def9e0..0526f21 100644
--- a/fxjs/BUILD.gn
+++ b/fxjs/BUILD.gn
@@ -223,6 +223,7 @@
         "gc/heap.cpp",
         "gc/heap.h",
       ]
+      configs += [ "../:pdfium_core_config" ]
       deps = [
         "../core/fxcrt",
         "//v8:v8_libplatform",