checkpatch: use utf-8 match for spell checking

The current code that checks for misspelling verifies, in a more
complex regex, if $rawline matches [^\w]($misspellings)[^\w]

Being $rawline a byte-string, a utf-8 character in $rawline can
match the non-word-char [^\w].
E.g.:
	./scripts/checkpatch.pl --git 81c2f05
	WARNING: 'ment' may be misspelled - perhaps 'meant'?
	torvalds#36: FILE: MAINTAINERS:14360:
	+M:     Clément Léger <[email protected]>
	            ^^^^

Use a utf-8 version of $rawline for spell checking.

Change-Id: I8dcd93979cd1c39186c750e588038f4a1e374bf1
Signed-off-by: Antonio Borneo <[email protected]>
Reported-by: Clément Le Goffic <[email protected]>
Reviewed-on: https://gerrit.st.com/c/mpu/oe/st/linux-stm32/+/372873
Tested-by: Clement LE GOFFIC <[email protected]>
ACI: CIBUILD <[email protected]>
Reviewed-by: Clement LE GOFFIC <[email protected]>
Domain-Review: Amelie DELAUNAY <[email protected]>

Author: Antonio Borneo

Diff for: scripts/checkpatch.pl

@@ -3490,9 +3490,10 @@ sub process {
 # Check for various typo / spelling mistakes
 		if (defined($misspellings) &&
 		    ($in_commit_log || $line =~ /^(?:\+|Subject:)/i)) {
-			while ($rawline =~ /(?:^|[^\w\-'`])($misspellings)(?:[^\w\-'`]|$)/gi) {
+			my $rawline_utf8 = decode("utf8", $rawline);
+			while ($rawline_utf8 =~ /(?:^|[^\w\-'`])($misspellings)(?:[^\w\-'`]|$)/gi) {
 				my $typo = $1;
-				my $blank = copy_spacing($rawline);
+				my $blank = copy_spacing($rawline_utf8);
 				my $ptr = substr($blank, 0, $-[1]) . "^" x length($typo);
 				my $hereptr = "$hereline$ptr\n";
 				my $typo_fix = $spelling_fix{lc($typo)};