Fix sgml and tex regex against perl-5.22. See Gentoo-bug: 604428.
Based on a patch from upstream git. Original commit info:
From 44e5c2f02b3166536257bc9d6384d41dda386648 Mon Sep 17 00:00:00 2001
From: Martin Quinson <martin.quinson@loria.fr>
Date: Fri, 28 Aug 2015 19:01:17 +0200
Subject: [PATCH] Port our regex to Perl 5.22 (patch by Roderich Schupp)

---
 lib/Locale/Po4a/Sgml.pm | 4 ++--
 lib/Locale/Po4a/TeX.pm  | 2 +-
 2 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/lib/Locale/Po4a/Sgml.pm b/lib/Locale/Po4a/Sgml.pm
index 742e003..3ad5e8d 100644
--- a/lib/Locale/Po4a/Sgml.pm
+++ b/lib/Locale/Po4a/Sgml.pm
@@ -672,9 +672,9 @@ sub parse_file {
             }
         }
     }
-    $prolog =~ s/<!--{PO4A-ent-beg-(.*?)}(.*?){PO4A-ent-end}-->/<!ENTITY % $1 SYSTEM "$2">/g;
+    $prolog =~ s/<!--\{PO4A-ent-beg-(.*?)\}(.*?)\{PO4A-ent-end\}-->/<!ENTITY % $1 SYSTEM "$2">/g;
     # Unprotect undefined inclusions, and die of them
-    $prolog =~ s/{PO4A-percent}/%/sg;
+    $prolog =~ s/\{PO4A-percent\}/%/sg;
     if ($prolog =~ /%([^;\s]*);/) {
         die wrap_mod("po4a::sgml",
                      dgettext("po4a",
diff --git a/lib/Locale/Po4a/TeX.pm b/lib/Locale/Po4a/TeX.pm
index a78f94b..0faa465 100644
--- a/lib/Locale/Po4a/TeX.pm
+++ b/lib/Locale/Po4a/TeX.pm
@@ -1168,7 +1168,7 @@ sub parse {
 #       environment contains an un-closed bracket)
         if (   ($closed and ($line =~ /^\s*$/ or
                              $line =~ /^\s*$RE_VERBATIM\s*$/))
-            or (in_verbatim(@env) and $line =~ /^\s*\Q$ESCAPE\Eend{$env[-1]}\s*$/)
+            or (in_verbatim(@env) and $line =~ /^\s*\Q$ESCAPE\Eend\{$env[-1]\}\s*$/)
            ) {
             # An empty line. This indicates the end of the current
             # paragraph.
-- 
2.10.2