glibc/include/alloca.h

#ifndef _ALLOCA_H

#include <stdlib/alloca.h>

#undef	__alloca

/* Now define the internal interfaces.  */
extern void *__alloca (size_t __size);

#ifdef	__GNUC__
# define __alloca(size)	__builtin_alloca (size)
#endif /* GCC.  */

#endif