[build] Disable warning for deprecated declaration (#3270)

Add "-Wno-deprecated-declarations" to cflags. The deprecated declaration
warning breaks builds in some Linux and Android build environments.

b/330363799

Change-Id: I9c0cfc5e2ca9fa4241c6d866b5946b13e31e2545

starboard/build/config/BUILD.gn

@@ -34,6 +34,7 @@ if (cobalt_pending_clean_up) {
     if (is_clang) {
       cflags = [
         "-Wno-c99-designator",
+        "-Wno-deprecated-declarations",
         "-Wno-ignored-qualifiers",
         "-Wno-implicit-fallthrough",
         "-Wno-inconsistent-missing-override",