Convert third_party source sets to static libraries.

third_party/ots/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("ots_config") {
   include_dirs = [ "include" ]
 }
 
-source_set("ots") {
+static_library("ots") {
   sources = [
     "include/opentype-sanitiser.h",
     "include/ots-memory-stream.h",
     "src/cff.cc",
     "src/cff.h",
     "src/cff_type2_charstring.cc",
     "src/cff_type2_charstring.h",
     "src/cmap.cc",
     "src/cmap.h",
     "src/cvt.cc",
@@ skipping 71 matching lines @@
 fuzzer_test("ots_fuzzer") {
   sources = [
     "fuzz/ots_fuzzer.cc",
   ]
   deps = [
     ":ots",
   ]
   libfuzzer_options = [ "max_len=16800" ]
   seed_corpus = "//third_party/harfbuzz-ng/fuzz/seed_corpus"
 }