Reland of Pass -Oz flag to Clang when targeting Android.

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 a2c2d0c637c6d8a248204551c346ad2de4f4c005..1ae296d66003facfe504a667b2eb398ddb173465 100644
--- a/third_party/expat/BUILD.gn
+++ b/third_party/expat/BUILD.gn
@@ -33,6 +33,11 @@
 
     public_configs = [ ":expat_config" ]
 
+    # TODO(thakis): Remove this once clang no longer crashes when building
+    # libexpat with -Oz.
+    configs -= [ "//build/config/compiler:default_optimization" ]
+    configs += [ "//build/config/compiler:optimize_max" ]
+
     defines = [ "_LIB" ]
     if (is_win) {
       defines += [ "COMPILED_FROM_DSP" ]