include/stddef: define SIZE_MAX

It's needed for future work.

Change-Id: I3419d11072bc0e3791ad08144c2a25c607550f28
Signed-off-by: Patrick Georgi <patrick@coreboot.org>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/78269
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Julius Werner <jwerner@chromium.org>
Reviewed-by: Kyösti Mälkki <kyosti.malkki@gmail.com>

src/include/stddef.h

@@ -7,6 +7,7 @@
 
 typedef __PTRDIFF_TYPE__ ptrdiff_t;
 typedef __SIZE_TYPE__ size_t;
+#define SIZE_MAX __SIZE_MAX__
 /* There is a GCC macro for a size_t type, but not
  * for a ssize_t type. Below construct tricks GCC
  * into making __SIZE_TYPE__ signed.