libpayload: add kconfig.h

This implements the linux kernel's macros to handle
boolean CONFIG_ variables more easily.

Change-Id: I595f9db652d019fe72e231111258ec609bec9d4e
Signed-off-by: Stefan Reinauer <reinauer@google.com>
Reviewed-on: http://review.coreboot.org/2036
Tested-by: build bot (Jenkins)
Reviewed-by: Ronald G. Minnich <rminnich@gmail.com>

payloads/libpayload/include/kconfig.h

@@ -0,0 +1,21 @@
+#ifndef __KCONFIG_H__
+#define __KCONFIG_H__
+
+#include <libpayload-config.h>
+
+/*
+ * Getting something that works in C and CPP for an arg that may or may
+ * not be defined is tricky.  Here, if we have "#define CONFIG_BOOGER 1"
+ * we match on the placeholder define, insert the "0," for arg1 and generate
+ * the triplet (0, 1, 0).  Then the last step cherry picks the 2nd arg (a one).
+ * When CONFIG_BOOGER is not defined, we generate a (... 1, 0) pair, and when
+ * the last step cherry picks the 2nd arg, we get a zero.
+ */
+#define __ARG_PLACEHOLDER_1 0,
+#define config_enabled(cfg) _config_enabled(cfg)
+#define _config_enabled(value) __config_enabled(__ARG_PLACEHOLDER_##value)
+#define __config_enabled(arg1_or_junk) ___config_enabled(arg1_or_junk 1, 0, 0)
+#define ___config_enabled(__ignored, val, ...) val
+
+#define IS_ENABLED(option) config_enabled(option)
+#endif