[cpp] Suppress -Wextra-semi

Bug: 56257
Change-Id: I4ff71389ca5b9d4cefe891092291971c7ed6eaa1
Reviewed-on: https://fuchsia-review.googlesource.com/c/third_party/github.com/google/cppdap/+/600643
Reviewed-by: Tamir Duberstein <tamird@google.com>

BUILD.gn

diff --git a/BUILD.gn b/BUILD.gn
index 1f9f24f..12dfe13 100644
--- a/BUILD.gn
+++ b/BUILD.gn
@@ -31,6 +31,9 @@
 
   cflags = [ "-DCPPDAP_JSON_RAPID" ]
 
+  # Suppress warnings that Fuchsia build adds
+  cflags += [ "-Wno-extra-semi" ]
+
   public_configs = [ ":includes" ]
 
   deps = [ "//third_party/rapidjson" ]