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

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

scripts/checkpatch.pl

@@ -1,4 +1,4 @@
-#!/usr/bin/perl -w
+#!/usr/bin/env perl 
 # (c) 2001, Dave Jones. (the file handling bit)
 # (c) 2005, Joel Schopp <jschopp@austin.ibm.com> (the ugly bit)
 # (c) 2007,2008, Andy Whitcroft <apw@uk.ibm.com> (new conditions, test suite)
@@ -7,6 +7,7 @@
 # Licensed under the terms of the GNU GPL License version 2
 
 use strict;
+use warnings;
 
 my $P = $0;
 $P =~ s@.*/@@g;