checkpatch: fix TYPO_SPELLING check for words with apostrophe

checkpatch reports a false TYPO_SPELLING warning for some words containing
an apostrophe when run with --codespell option.

A false positive is "doesn't".  Occurrence of the word causes checkpatch
to emit the following warning:

"WARNING: 'doesn'' may be misspelled - perhaps 'doesn't'?"

Modify the regex pattern to be more in line with the codespell default
word matching regex.  This fixes the word capture and avoids the false
warning.

In addition, highlight the misspelled word location by adding a caret
below the word.

[[email protected]: make matched misspelling more obvious, per Joe]
  Link: https://lkml.kernel.org/r/[email protected]

Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Dwaipayan Ray <[email protected]>
Suggested-by: Joe Perches <[email protected]>
Reported-by: Peilin Ye <[email protected]>
Acked-by: Joe Perches <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

scripts/checkpatch.pl

@@ -2746,15 +2746,18 @@ sub process {
 # Check for various typo / spelling mistakes
 		if (defined($misspellings) &&
 		    ($in_commit_log || $line =~ /^(?:\+|Subject:)/i)) {
-			while ($rawline =~ /(?:^|[^a-z@])($misspellings)(?:\b|$|[^a-z@])/gi) {
+			while ($rawline =~ /(?:^|[^\w\-'`])($misspellings)(?:[^\w\-'`]|$)/gi) {
 				my $typo = $1;
+				my $blank = copy_spacing($rawline);
+				my $ptr = substr($blank, 0, $-[1]) . "^" x length($typo);
+				my $hereptr = "$hereline$ptr\n";
 				my $typo_fix = $spelling_fix{lc($typo)};
 				$typo_fix = ucfirst($typo_fix) if ($typo =~ /^[A-Z]/);
 				$typo_fix = uc($typo_fix) if ($typo =~ /^[A-Z]+$/);
 				my $msg_level = \&WARN;
 				$msg_level = \&CHK if ($file);
 				if (&{$msg_level}("TYPO_SPELLING",
-						  "'$typo' may be misspelled - perhaps '$typo_fix'?\n" . $herecurr) &&
+						  "'$typo' may be misspelled - perhaps '$typo_fix'?\n" . $hereptr) &&
 				    $fix) {
 					$fixed[$fixlinenr] =~ s/(^|[^A-Za-z@])($typo)($|[^A-Za-z@])/$1$typo_fix$3/;
 				}