build: avoid tabs that failed syntax-check

Introduced in commit f299ddd6.

* src/check-symfile.pl: Fix whitespace.
* .dir-locals.el (perl-mode): Prevent future occurrences.

.dir-locals.el

@@ -14,4 +14,7 @@
  (nxml-mode . (
 	       (indent-tabs-mode . nil)
 	       ))
+ (perl-mode . (
+	       (indent-tabs-mode . nil)
+	       ))
  )

src/check-symfile.pl

@@ -24,10 +24,10 @@ while (<SYMFILE>) {
     die "malformed line $_" unless /^\s*(\S+);$/;
 
     if (exists $wantsyms{$1}) {
-	print STDERR "Symbol $1 is listed twice\n";
-	$ret = 1;
+        print STDERR "Symbol $1 is listed twice\n";
+        $ret = 1;
     } else {
-	$wantsyms{$1} = 1;
+        $wantsyms{$1} = 1;
     }
 }
 close SYMFILE;