uapi: stddef.h: Provide UAPI macros for __counted_by_{le, be}

This commit can be considered an addition to commit ca7e324e
("compiler_types: add Endianness-dependent __counted_by_{le,be}") [1].

In the commit referenced above the __counted_by_{le,be}() attributes
were defined based on platform's endianness with the goal to that the
structures contain flexible arrays at the end, and the counter for,
can be annotated with these attributes.

So, this commit only provide UAPI macros for UAPI structs that will
gain annotations for __counted_by_{le, be} attributes. And it is the
previous step to be able to use these attributes in UAPI.

Link: https://lore.kernel.org/r/20240327142241.1745989-2-aleksander.lobakin@intel.comSuggested-by: Sven Eckelmann <sven@narfation.org>
Signed-off-by: Erick Archer <erick.archer@outlook.com>
Link: https://lore.kernel.org/r/AS8PR02MB72372E45071E8821C07236F78BE42@AS8PR02MB7237.eurprd02.prod.outlook.com
Fixes: ca7e324e ("compiler_types: add Endianness-dependent __counted_by_{le,be}")
Signed-off-by: Kees Cook <keescook@chromium.org>

include/uapi/linux/stddef.h

@@ -55,4 +55,12 @@
 #define __counted_by(m)
 #endif
 
+#ifndef __counted_by_le
+#define __counted_by_le(m)
+#endif
+
+#ifndef __counted_by_be
+#define __counted_by_be(m)
+#endif
+
 #endif /* _UAPI_LINUX_STDDEF_H */