stddef.h: Disable check_member() macro when compiling with CLANG

CLANG assumes that _Static_assert() is a C++11 only feature and
errs out when encountering the check_member macro complaining about
a reinterpret_cast.

Change-Id: Id8c6b47b4f5716e6184aec9e0bc4b0e1c7aaf17c
Signed-off-by: Stefan Reinauer <stefan.reinauer@coreboot.org>
Reviewed-on: http://review.coreboot.org/10827
Reviewed-by: Patrick Georgi <pgeorgi@google.com>
Tested-by: build bot (Jenkins)

src/include/stddef.h

@@ -32,9 +32,13 @@ typedef unsigned int wint_t;
 
 #define offsetof(TYPE, MEMBER) ((size_t) &((TYPE *)0)->MEMBER)
 
+#if !defined(__clang__)
 #define check_member(structure, member, offset) _Static_assert( \
 	offsetof(struct structure, member) == offset, \
 	"`struct " #structure "` offset for `" #member "` is not " #offset )
+#else
+#define check_member(structure, member, offset)
+#endif
 
 /**
  * container_of - cast a member of a structure out to the containing structure