checkpatch: add check for line continuations in quoted strings

Add a warning for unterminated quoted strings with line continuations as
these frequently add unwanted whitespace.

Signed-off-by: Joe Perches <joe@perches.com>
Cc: Andy Whitcroft <apw@canonical.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

scripts/checkpatch.pl

@@ -2748,6 +2748,11 @@ sub process {
 			WARN("sizeof(& should be avoided\n" . $herecurr);
 		}
 
+# check for line continuations in quoted strings with odd counts of "
+		if ($rawline =~ /\\$/ && $rawline =~ tr/"/"/ % 2) {
+			WARN("Avoid line continuations in quoted strings\n" . $herecurr);
+		}
+
 # check for new externs in .c files.
 		if ($realfile =~ /\.c$/ && defined $stat &&
 		    $stat =~ /^.\s*(?:extern\s+)?$Type\s+($Ident)(\s*)\(/s)