trace_processor: fix compile and build on fuzzer

Change-Id: I87ae5c9cfa5adb2104b360274ed5b852148a604d
diff --git a/gn/standalone/BUILD.gn b/gn/standalone/BUILD.gn
index c52b7c1..79cdadf 100644
--- a/gn/standalone/BUILD.gn
+++ b/gn/standalone/BUILD.gn
@@ -23,6 +23,12 @@
     "-Wpedantic",
   ]
 
+  # Disable variadic macro warning as we make extensive use of them in trace
+  # processor and client API.
+  if (is_clang) {
+    cflags += [ "-Wno-gnu-zero-variadic-macro-arguments" ]
+  }
+
   # Disable Weverything on fuzzers to avoid breakages when new versions of clang
   # are rolled into OSS-fuzz.
   if (is_clang && !is_fuzzer) {
@@ -33,7 +39,6 @@
       "-Wno-disabled-macro-expansion",
       "-Wno-gnu-include-next",
       "-Wno-gnu-statement-expression",
-      "-Wno-gnu-zero-variadic-macro-arguments",
       "-Wno-padded",
       "-Wno-reserved-id-macro",
       "-Wno-unknown-sanitizers",