Convert third_party source sets to static libraries.

third_party/hunspell/BUILD.gn

 # Copyright 2014 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 import("//testing/libfuzzer/fuzzer_test.gni")
 
 config("hunspell_config") {
   defines = [
     "HUNSPELL_STATIC",
     "HUNSPELL_CHROME_CLIENT",
     "USE_HUNSPELL",
   ]
 }
 
 config("hunspell_warnings") {
   if (is_clang) {
     cflags = [ "-Wno-unused-private-field" ]
   }
 }
 
-source_set("hunspell") {
+static_library("hunspell") {
   sources = [
     "google/bdict.cc",
     "google/bdict.h",
     "google/bdict_reader.cc",
     "google/bdict_reader.h",
     "google/bdict_writer.cc",
     "google/bdict_writer.h",
     "src/hunspell/affentry.cxx",
     "src/hunspell/affentry.hxx",
     "src/hunspell/affixmgr.cxx",
@@ skipping 85 matching lines @@
     "fuzz/hunspell_fuzzer.cc",
     "fuzz/hunspell_fuzzer_hunspell_dictionary.h",
   ]
   deps = [
     ":hunspell",
   ]
 
   # This is a dictionary for the fuzzer, not a spellcheck dictionary.
   dict = "fuzz/hunspell.dict"
 }