Conditionally link protobuf for fuzzer builds.

BUG=chromium:1017318
TEST=cros_workon-amd64-generic start update_engine && \
  USE='asan fuzzer kvm_guest' ./build_packages \
    --board=amd64-generic --skip_chroot_upgrade chromium-os-fuzzers

Change-Id: I696c8bdf20e4a60d21139c169ac90ede186f4050
Reviewed-on: https://chromium-review.googlesource.com/c/aosp/platform/system/update_engine/+/1881336
Tested-by: Allen Webb <allenwebb@google.com>
Reviewed-by: Amin Hassani <ahassani@chromium.org>
Commit-Queue: Allen Webb <allenwebb@google.com>
diff --git a/BUILD.gn b/BUILD.gn
index 01207bd..0cc27e6 100644
--- a/BUILD.gn
+++ b/BUILD.gn
@@ -96,8 +96,12 @@
     # before protobuf here or the linker flags won't be in the right
     # order.
     "system_api",
-    "protobuf-lite",
   ]
+  if (use.fuzzer) {
+    pkg_deps += [ "protobuf" ]
+  } else {
+    pkg_deps += [ "protobuf-lite" ]
+  }
 }
 
 # Protobufs.