This patch fixes a regex parsing compatibility issue with Perl 5.26.0.
It manifests during the configure phase of at-spi2-core like this:

------
Unescaped left brace in regex is illegal here in regex; marked by <-- HERE in m/^(.*)\${ <-- HERE ?([A-Z_]+)}?(.*)$/ at /gnu/store/...-intltool-0.51.0/bin/intltool-update line 1065.
------

Copied from Gentoo and MSYS2:

https://gitweb.gentoo.org/repo/gentoo.git/tree/dev-util/intltool/files/intltool-0.51.0-perl-5.26.patch?id=1105187fc65d8bf643e682fcef39620dcfd9326a
https://github.com/Alexpux/MSYS2-packages/blob/0d3f442553ae4fc8798e32cbf44c4252fa8f3c07/intltool/perl-5.22-compatibility.patch

#diff -ruN intltool-0.51.0.orig/intltool-update.in intltool-0.51.0/intltool-update.in
#--- intltool-0.51.0.orig/intltool-update.in	2017-06-28 00:47:20.889269294 +0200
#+++ intltool-0.51.0/intltool-update.in	2017-06-28 00:48:14.592271529 +0200
#@@ -1068,7 +1068,7 @@
# 	my $untouched = $1;
# 	my $sub = "";
#         # Ignore recursive definitions of variables
#-        $sub = $varhash{$2} if defined $varhash{$2} and $varhash{$2} !~ /\${?$2}?/;
#+        $sub = $varhash{$2} if defined $varhash{$2} and $varhash{$2} !~ /\$\{?$2}?/;
# 
# 	return SubstituteVariable ("$untouched$sub$rest");
#     }
--- intltool-0.51.0.orig/intltool-update.in	2015-03-09 02:39:54.000000000 +0100
+++ intltool-0.51.0.orig/intltool-update.in	2015-06-19 01:52:07.171228154 +0200
@@ -1062,7 +1062,7 @@ 
 	}
     }
 
-    if ($str =~ /^(.*)\${?([A-Z_]+)}?(.*)$/)
+    if ($str =~ /^(.*)\$\{?([A-Z_]+)}?(.*)$/)
     {
 	my $rest = $3;
 	my $untouched = $1;
@@ -1068,7 +1068,7 @@
 	my $untouched = $1;
 	my $sub = "";
         # Ignore recursive definitions of variables
-        $sub = $varhash{$2} if defined $varhash{$2} and $varhash{$2} !~ /\${?$2}?/;
+        $sub = $varhash{$2} if defined $varhash{$2} and $varhash{$2} !~ /\$\{?$2}?/;
 
 	return SubstituteVariable ("$untouched$sub$rest");
     }
@@ -1190,10 +1190,10 @@ 
 	$name    =~ s/\(+$//g;
 	$version =~ s/\(+$//g;
 
-	$varhash{"PACKAGE_NAME"} = $name if (not $name =~ /\${?AC_PACKAGE_NAME}?/);
-	$varhash{"PACKAGE"} = $name if (not $name =~ /\${?PACKAGE}?/);
-	$varhash{"PACKAGE_VERSION"} = $version if (not $name =~ /\${?AC_PACKAGE_VERSION}?/);
-	$varhash{"VERSION"} = $version if (not $name =~ /\${?VERSION}?/);
+	$varhash{"PACKAGE_NAME"} = $name if (not $name =~ /\$\{?AC_PACKAGE_NAME}?/);
+	$varhash{"PACKAGE"} = $name if (not $name =~ /\$\{?PACKAGE}?/);
+	$varhash{"PACKAGE_VERSION"} = $version if (not $name =~ /\$\{?AC_PACKAGE_VERSION}?/);
+	$varhash{"VERSION"} = $version if (not $name =~ /\$\{?VERSION}?/);
     }
 
     if ($conf_source =~ /^AC_INIT\(([^,\)]+),([^,\)]+)[,]?([^,\)]+)?/m)
@@ -1219,11 +1219,11 @@ 
 	$version =~ s/\(+$//g;
         $bugurl  =~ s/\(+$//g if (defined $bugurl);
 
-	$varhash{"PACKAGE_NAME"} = $name if (not $name =~ /\${?AC_PACKAGE_NAME}?/);
-	$varhash{"PACKAGE"} = $name if (not $name =~ /\${?PACKAGE}?/);
-	$varhash{"PACKAGE_VERSION"} = $version if (not $name =~ /\${?AC_PACKAGE_VERSION}?/);
-	$varhash{"VERSION"} = $version if (not $name =~ /\${?VERSION}?/);
-        $varhash{"PACKAGE_BUGREPORT"} = $bugurl if (defined $bugurl and not $bugurl =~ /\${?\w+}?/);
+	$varhash{"PACKAGE_NAME"} = $name if (not $name =~ /\$\{?AC_PACKAGE_NAME}?/);
+	$varhash{"PACKAGE"} = $name if (not $name =~ /\$\{?PACKAGE}?/);
+	$varhash{"PACKAGE_VERSION"} = $version if (not $name =~ /\$\{?AC_PACKAGE_VERSION}?/);
+	$varhash{"VERSION"} = $version if (not $name =~ /\$\{?VERSION}?/);
+        $varhash{"PACKAGE_BUGREPORT"} = $bugurl if (defined $bugurl and not $bugurl =~ /\$\{?\w+}?/);
     }
 
     # \s makes this not work, why?
t/AUTHORS?id=1cf0814d4d89737d7a61bc64650ea5ac58fff7cb'>Add Paul to 'AUTHORS'.</a></td><td>Mark H Weaver</td></tr>
<tr><td><span title='2015-03-09 23:51:43 +0100'>2015-03-09</span></td><td><a href='/guix/commit/AUTHORS?id=e92da92d63d0b50d462fc3608b19d18ac239d87b'>Add Alexander to 'AUTHORS'.</a></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2015-02-20 10:14:23 +0100'>2015-02-20</span></td><td><a href='/guix/commit/AUTHORS?id=76aae0f96f3aed10e842b1726ffc19848600c04d'>Add David Hashe to 'AUTHORS'.</a></td><td>Andreas Enge</td></tr>
<tr><td><span title='2015-02-02 12:46:35 +0100'>2015-02-02</span></td><td><a href='/guix/commit/AUTHORS?id=1af50c224d7d8febad0cf34b67d0ffd6c2dff638'>Add Deck to 'AUTHORS'.</a></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2015-01-24 22:57:49 +0100'>2015-01-24</span></td><td><a href='/guix/commit/AUTHORS?id=da74bc7886cba77192260d84b2dd57466e4b5354'>Add Ricardo to 'AUTHORS'.</a></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2014-12-09 13:19:47 +0100'>2014-12-09</span></td><td><a href='/guix/commit/AUTHORS?id=03356e977567b76e981c04af20302018f9f02fac'>Add Tomáš to 'AUTHORS'.</a></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2014-11-18 22:03:03 +0100'>2014-11-18</span></td><td><a href='/guix/commit/AUTHORS?id=418367f7f0d209b6a1251ab8e33c5233dd099a26'>Add Julien to 'AUTHORS'.</a></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2014-11-14 22:58:18 +0100'>2014-11-14</span></td><td><a href='/guix/commit/AUTHORS?id=f21ca31d15a7a9bd8aaf221c0a2c97b2d08980e9'>Add the name of Sou Bunnbu in its original script to 'AUTHORS'.</a></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2014-11-12 14:39:30 +0100'>2014-11-12</span></td><td><a href='/guix/commit/AUTHORS?id=dc05f01cba88bc768a0b12ecfb3760073ff0bc47'>Add Sun Bunnbu to 'AUTHORS'.</a></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2014-10-26 14:48:57 +0100'>2014-10-26</span></td><td><a href='/guix/commit/AUTHORS?id=822efdff8a52ba50a84a6f138e22468dc824174b'>Update name and email address for Joshua Grant.</a></td><td>Joshua Grant</td></tr>
<tr><td><span title='2014-10-08 22:12:06 +0200'>2014-10-08</span></td><td><a href='/guix/commit/AUTHORS?id=9c814b828ae07899594ad9cd83d2e77e4cc528cc'>Add Federico to 'AUTHORS'.</a></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2014-09-10 15:44:51 +0200'>2014-09-10</span></td><td><a href='/guix/commit/AUTHORS?id=6e4532e8fec5b31fad38be82ada46b5a70952b91'>Add Marek to 'AUTHORS'.</a></td><td>Ludovic Courtès</td></tr>