checkpatch: enforce sane perl version

I got a bug report from a couple of users who said checkpatch.pl was
broken for them.  It was erroring out on fairly random lines most commonly
with messages like:

	Nested quantifiers in regex; marked by <--HERE in m/(\((?:[^\(\)]++ <-- HERE |(?-1))*\))/ at ./checkpatch.pl line 340.

The bug reporter was running a version of perl 5.8 which was end-of-lifed
in 2008: http://www.cpan.org/src/.  Versions of perl this old are at
_best_ quite untested.  At worst, they are crusty and known to be
completely broken.

If folks have a system _that_ old, then we should have mercy on them and
give them a half-decent error message rather than fail with nutty error
messages.

This patch enforces that checkpatch.pl is run with perl 5.10, which was
end-of-lifed in 2009.  The new --ignore-perl-version command-line switch
will let folks override this if they want.

Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Joe Perches <joe@perches.com>
Cc: Andy Whitcroft <apw@shadowen.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

scripts/checkpatch.pl

@@ -37,6 +37,8 @@
 my $help = 0;
 my $configuration_file = ".checkpatch.conf";
 my $max_line_length = 80;
+my $ignore_perl_version = 0;
+my $minimum_perl_version = 5.10.0;
 
 sub help {
 	my ($exitcode) = @_;
@@ -71,6 +73,8 @@ sub help {
                              "<inputfile>.EXPERIMENTAL-checkpatch-fixes"
                              with potential errors corrected to the preferred
                              checkpatch style
+  --ignore-perl-version      override checking of perl version.  expect
+                             runtime errors.
   -h, --help, --version      display this help and exit
 
 When FILE is - read standard input.
@@ -123,6 +127,7 @@ sub help {
 	'mailback!'	=> \$mailback,
 	'summary-file!'	=> \$summary_file,
 	'fix!'		=> \$fix,
+	'ignore-perl-version!' => \$ignore_perl_version,
 	'debug=s'	=> \%debug,
 	'test-only=s'	=> \$tst_only,
 	'h|help'	=> \$help,
@@ -133,6 +138,13 @@ sub help {
 
 my $exit = 0;
 
+if ($^V && $^V lt $minimum_perl_version) {
+	printf "$P: requires at least perl version %vd\n", $minimum_perl_version;
+	if (!$ignore_perl_version) {
+		exit(1);
+	}
+}
+
 if ($#ARGV < 0) {
 	print "$P: no input files\n";
 	exit(1);