gnu: acl: Fix test regression with perl-5.26.

* gnu/packages/acl.scm (acl)[source]: Add patch.
* gnu/packages/patches/acl-fix-perl-regex.patch: New file.
* gnu/local.mk (dist_patch_DATA): Register it.

gnu/packages/patches/acl-fix-perl-regex.patch

@@ -0,0 +1,22 @@
+This can be removed with the next acl release
+
+---
+ test/run | 2 +-
+ 1 file changed, 1 insertion(+), 1 deletion(-)
+
+diff --git a/test/run b/test/run
+index 2cf52e8..4627cd2 100755
+--- a/test/run
++++ b/test/run
+@@ -70,7 +70,7 @@ for (;;) {
+   if (defined $line) {
+     # Substitute %VAR and %{VAR} with environment variables.
+     $line =~ s[%(\w+)][$ENV{$1}]eg;
+-    $line =~ s[%{(\w+)}][$ENV{$1}]eg;
++    $line =~ s[%\{(\w+)\}][$ENV{$1}]eg;
+   }
+   if (defined $line) {
+     if ($line =~ s/^\s*< ?//) {
+-- 
+2.15.0
+