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?
ix/commit/tests/gem.scm?id=a34b236c17f5f7a29c3ce05766071b57e8cdb271'>import: Importers return prefixed licenses.</a><span class='msg-avail'>...</span></td><td>David Craven</td></tr>
<tr><td><span title='2016-04-03 14:19:09 +0200'>2016-04-03</span></td><td><a href='/guix/commit/tests/gem.scm?id=a9edb211e733b8b34e67ec3b4450567e9376986f'>build: Add a Guile custom test driver using SRFI-64.</a><span class='msg-avail'>...</span></td><td>Mathieu Lirzin</td></tr>
<tr><td><span title='2016-01-20 21:52:52 +1000'>2016-01-20</span></td><td><a href='/guix/commit/tests/gem.scm?id=e88d5fa9ebab07d0b23cb3fc0f3f38bd41047e94'>import: gem: Beautify only the description, not the synopsis.</a><span class='msg-avail'>...</span></td><td>Ben Woodcroft</td></tr>
<tr><td><span title='2015-09-01 20:00:01 -0400'>2015-09-01</span></td><td><a href='/guix/commit/tests/gem.scm?id=a96524cc7d302ad6a8f2cd2e970a148b360f629a'>import: gem: Fix minor bug and add unit test.</a><span class='msg-avail'>...</span></td><td>David Thompson</td></tr>