This patch adds an include needed since icu59:
Source: https://git.archlinux.org/svntogit/community.git/plain/trunk/icu59.patch?h=packages/aegisub
--- aegisub-3.2.2/src/utils.cpp	2014-12-08 02:07:09.000000000 +0200
+++ aegisub-3.2.2/src/utils.cpp	2017-04-26 11:11:15.438239182 +0300
@@ -44,6 +44,7 @@
 #include <boost/filesystem/path.hpp>
 #include <map>
 #include <unicode/locid.h>
+#include <unicode/unistr.h>
 #include <wx/clipbrd.h>
 #include <wx/filedlg.h>
 #include <wx/stdpaths.h>
