Update the defines to compile against newer sysroot

_BSD_SOURCE is deprecated, use _ALL_SOURCE and _GNU_SOURCE instead.

Change-Id: I8ac1209379afb10f04dbbc59eeaedd734f2a6aed
Reviewed-on: https://fuchsia-review.googlesource.com/c/third_party/iperf/+/583746
Reviewed-by: Roland McGrath <mcgrathr@google.com>
diff --git a/BUILD.gn b/BUILD.gn
index 8ed648a..7273bc3 100644
--- a/BUILD.gn
+++ b/BUILD.gn
@@ -83,8 +83,8 @@
     "src/units.c",
   ]
   defines = [
-    "_BSD_SOURCE",
-    "_POSIX_C_SOURCE=200809L",
+    "_ALL_SOURCE",
+    "_GNU_SOURCE",
   ]
   cflags_c = [
     "-Wno-format",