checkpatch: add --strict test for switch/default missing break

switch default case is sometimes written as "default:;".  This can cause
new cases added below the default to be defective.

Suggest adding a break; after empty default cases to avoid fallthrough
defects.

Fixed indentation in the other semicolon test above it.
Suggested-by: NPeter Senna Tschudin <peter.senna@gmail.com>
Signed-off-by: NJoe Perches <joe@perches.com>
Cc: Andy Whitcroft <apw@canonical.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

scripts/checkpatch.pl

@@ -3448,8 +3448,22 @@ sub process {
 
 # check for multiple semicolons
 		if ($line =~ /;\s*;\s*$/) {
-		    WARN("ONE_SEMICOLON",
-			 "Statements terminations use 1 semicolon\n" . $herecurr);
+			WARN("ONE_SEMICOLON",
+			     "Statements terminations use 1 semicolon\n" . $herecurr);
+		}
+
+# check for switch/default statements without a break;
+		if ($^V && $^V ge 5.10.0 &&
+		    defined $stat &&
+		    $stat =~ /^\+[$;\s]*(?:case[$;\s]+\w+[$;\s]*:[$;\s]*|)*[$;\s]*\bdefault[$;\s]*:[$;\s]*;/g) {
+			my $ctx = '';
+			my $herectx = $here . "\n";
+			my $cnt = statement_rawlines($stat);
+			for (my $n = 0; $n < $cnt; $n++) {
+				$herectx .= raw_line($linenr, $n) . "\n";
+			}
+			WARN("DEFAULT_NO_BREAK",
+			     "switch default: should use break\n" . $herectx);
 		}
 
 # check for gcc specific __FUNCTION__