Revert "Delete the v8_target_cpu/v8_current_cpu hack in the GN build."

build/toolchain/gcc_toolchain.gni

Index: build/toolchain/gcc_toolchain.gni
diff --git a/build/toolchain/gcc_toolchain.gni b/build/toolchain/gcc_toolchain.gni
index 94aac5bdc2fffde408e73de7329717f0f295cf4f..5ecabe5cdcef1cc7278d6bfe92d18203b23d2583 100644
--- a/build/toolchain/gcc_toolchain.gni
+++ b/build/toolchain/gcc_toolchain.gni
@@ -475,6 +475,12 @@ template("gcc_toolchain") {
         v8_current_cpu = current_cpu
       }
 
+      # TODO(crbug.com/625353) - Delete after v8 has been updated
+      # to only refer to v8_current_cpu. Until then, we need to make
+      # sure that v8_current_cpu always has the same value as v8_target_cpu,
+      # so that //build defines evaluate the way v8 is expecting them to.
+      v8_current_cpu = v8_target_cpu
+
       # Disable sanitizers for non-default toolchains.
       is_asan = false
       is_cfi = false