checkpatch: add test for possible misuse of IS_ENABLED() without CONFIG_

IS_ENABLED is almost always used with CONFIG_<FOO> defines.

Add a test to verify that the #define being tested starts with CONFIG_.

Signed-off-by: Joe Perches <joe@perches.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Reviewed-by: Kees Cook <keescook@chromium.org>
Link: http://lkml.kernel.org/r/e7fda760b91b769ba82844ba282d432c0d26d709.camel@perches.com
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

scripts/checkpatch.pl

@@ -6465,6 +6465,12 @@ sub process {
 			}
 		}
 
+# check for IS_ENABLED() without CONFIG_<FOO> ($rawline for comments too)
+		if ($rawline =~ /\bIS_ENABLED\s*\(\s*(\w+)\s*\)/ && $1 !~ /^CONFIG_/) {
+			WARN("IS_ENABLED_CONFIG",
+			     "IS_ENABLED($1) is normally used as IS_ENABLED(CONFIG_$1)\n" . $herecurr);
+		}
+
 # check for #if defined CONFIG_<FOO> || defined CONFIG_<FOO>_MODULE
 		if ($line =~ /^\+\s*#\s*if\s+defined(?:\s*\(?\s*|\s+)(CONFIG_[A-Z_]+)\s*\)?\s*\|\|\s*defined(?:\s*\(?\s*|\s+)\1_MODULE\s*\)?\s*$/) {
 			my $config = $1;