checkpatch: reduce is_maintained_obsolete lookup runtime

The is_maintained_obsolete function can be called twice using the same
filename.  This function spawns a process using get_maintainer.pl.
Store the status of each filename when spawned and use the stored result
to eliminate the spawning of unnecessary duplicate child processes.

Example:

old:

  $ time ./scripts/checkpatch.pl hp100-Move-to-staging.patch > /dev/null

  real	0m1.767s
  user	0m1.634s
  sys	0m0.141s

new:

  $ time ./scripts/checkpatch.pl hp100-Move-to-staging.patch > /dev/null

  real	0m1.184s
  user	0m1.085s
  sys	0m0.103s

Link: http://lkml.kernel.org/r/b982566a2b9b4825badce36fdfc3032bd0005151.camel@perches.comSigned-off-by: Joe Perches <joe@perches.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

scripts/checkpatch.pl

@@ -874,14 +874,18 @@ sub seed_camelcase_file {
 	}
 }
 
+our %maintained_status = ();
+
 sub is_maintained_obsolete {
 	my ($filename) = @_;
 
 	return 0 if (!$tree || !(-e "$root/scripts/get_maintainer.pl"));
 
-	my $status = `perl $root/scripts/get_maintainer.pl --status --nom --nol --nogit --nogit-fallback -f $filename 2>&1`;
+	if (!exists($maintained_status{$filename})) {
+		$maintained_status{$filename} = `perl $root/scripts/get_maintainer.pl --status --nom --nol --nogit --nogit-fallback -f $filename 2>&1`;
+	}
 
-	return $status =~ /obsolete/i;
+	return $maintained_status{$filename} =~ /obsolete/i;
 }
 
 sub is_SPDX_License_valid {