regen_perly: automatically touch perly.c

This forces 'perly.c' to be recompiled when you type 'make' after
changing 'perly.y'.

(This does not happen automatically because the changes to 'perly.y'
land in 'perly.act', which 'perly.c' includes but 'make' knows nothing
about. Thus, even if 'perly.act' has a newer mtime, 'make' won't update
'perly.o' if it already exists.)

Author: mauke

perly.act

@@ -169,6 +169,16 @@
     read_only_bottom_close_and_rename($_, ['regen_perly.pl', $y_file]);
 }
 
+{
+    (my $o_file = $y_file) =~ s/\.y$/.o/;
+    (my $c_file = $y_file) =~ s/\.y$/.c/;
+    if (-e $o_file) {
+        my $now = time;
+        utime $now, $now, $c_file
+            or warn "Can't touch $c_file: $!";
+    }
+}
+
 exit 0;