Add -Wno-write-strings

This is being turned on in the main repo.

Change-Id: Ic628b948f959a76854c9f3325580cdc1c4656cc5
Reviewed-on: https://fuchsia-review.googlesource.com/c/third_party/iperf/+/576485
Reviewed-by: Shai Barack <shayba@google.com>
diff --git a/BUILD.gn b/BUILD.gn
index 20904f5..8ed648a 100644
--- a/BUILD.gn
+++ b/BUILD.gn
@@ -94,6 +94,7 @@
     "-Wno-sign-compare",
     "-Wno-unused-but-set-parameter",
     "-Wno-unused-but-set-variable",
+    "-Wno-write-strings",
   ]
   if (is_fuchsia) {
     deps = [