build: remove absolute path to perl and replace with /usr/bin/env perl

Signed-off-by: Bastian Köcher <git@kchr.de>

scripts/cleanpatch

@@ -1,4 +1,4 @@
-#!/usr/bin/perl -w
+#!/usr/bin/env perl 
 #
 # Clean a patch file -- or directory of patch files -- of stealth whitespace.
 # WARNING: this can be a highly destructive operation.  Use with caution.
@@ -6,6 +6,7 @@
 
 use bytes;
 use File::Basename;
+use warnings;
 
 # Default options
 $max_width = 79;