[foozzie] Support multi-architecture builds

gni/v8.gni

Index: gni/v8.gni
diff --git a/gni/v8.gni b/gni/v8.gni
index c1a3b7cca9286fe6b90793fa21d9da6dc643c7c9..a4a36563061d7979529ccb5cd73b1c4482a21cb4 100644
--- a/gni/v8.gni
+++ b/gni/v8.gni
@@ -9,6 +9,9 @@ declare_args() {
   # Includes files needed for correctness fuzzing.
   v8_correctness_fuzzer = false
 
+  # Adds additional compile target for building multiple architectures at once.
+  v8_multi_arch_build = false
+
   # Indicate if valgrind was fetched as a custom deps to make it available on
   # swarming.
   v8_has_valgrind = false