includes: Provide wchar.h with wchar_t and wint_t

Change-Id: Iacb0e4eaf3f0b6bf843f3bfda5bdfde0f7a98808
Signed-off-by: Nico Huber <nico.huber@secunet.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/55590
Reviewed-by: Angel Pons <th3fanbus@gmail.com>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

payloads/libpayload/include/stddef.h

@@ -3,6 +3,13 @@
 
 #include <arch/types.h>
 
+#ifndef __WCHAR_TYPE__
+#define __WCHAR_TYPE__ int
+#endif
+#ifndef __cplusplus
+typedef __WCHAR_TYPE__ wchar_t;
+#endif
+
 #ifndef __SIZE_TYPE__
 #define __SIZE_TYPE__ unsigned long
 #endif