checkpatch: avoid COMMIT_LOG_LONG_LINE warning for signature tags

Currently checkpatch warns us for long lines in commits even for signature
tag lines.

Generally these lines exceed the 75-character limit because of:

 1) long names and long email address

 2) some comments on scoped review and acknowledgement, i.e., for a
    dedicated pointer on what was reported by the identity in
    'Reported-by'

 3) some additional comments on CC: stable@vger.org tags

Exclude signature tag lines from this class of warning.

There were 1896 COMMIT_LOG_LONG_LINE warnings in v5.6..v5.8 before this
patch application and 1879 afterwards.

A quick manual check found all the dropped warnings related to signature
tags.

Link: https://lkml.kernel.org/r/20201116083754.10629-1-yashsri421@gmail.com
Signed-off-by: Aditya Srivastava <yashsri421@gmail.com>
Acked-by: Joe Perches <joe@perches.com>
Cc: Lukas Bulwahn <lukas.bulwahn@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

scripts/checkpatch.pl

@@ -2952,8 +2952,8 @@ sub process {
 					# file delta changes
 		      $line =~ /^\s*(?:[\w\.\-]+\/)++[\w\.\-]+:/ ||
 					# filename then :
-		      $line =~ /^\s*(?:Fixes:|Link:)/i ||
-					# A Fixes: or Link: line
+		      $line =~ /^\s*(?:Fixes:|Link:|$signature_tags)/i ||
+					# A Fixes: or Link: line or signature tag line
 		      $commit_log_possible_stack_dump)) {
 			WARN("COMMIT_LOG_LONG_LINE",
 			     "Possible unwrapped commit description (prefer a maximum 75 chars per line)\n" . $herecurr);