Build expat from source when using afl_expat_xml_parse_fuzzer

third_party/expat/BUILD.gn

Index: third_party/expat/BUILD.gn
diff --git a/third_party/expat/BUILD.gn b/third_party/expat/BUILD.gn
index 642cd7ac2ddf2783cd724cbc0f0253e8847d735d..a2c2d0c637c6d8a248204551c346ad2de4f4c005 100644
--- a/third_party/expat/BUILD.gn
+++ b/third_party/expat/BUILD.gn
@@ -8,8 +8,8 @@ import("//testing/libfuzzer/fuzzer_test.gni")
 # On Linux, we implicitly already depend on expat via fontconfig;
 # let's not pull it in twice.
 # Chromecast doesn't ship expat as a system library.
-# Libfuzzer needs to build library from sources.
-if (is_linux && !is_chromecast && !use_libfuzzer) {
+# Libfuzzer and AFL need to build library from sources.
+if (is_linux && !is_chromecast && !use_libfuzzer && !use_afl) {
   config("expat_config") {
     libs = [ "expat" ]
   }