Does glibc have support for the five-arg form of mremap
on Linux? I couldn't find it...
#include <asm/unistd.h>
#define __NR_mremap2 __NR_mremap
_syscall5( void *, mremap2,
void *, old_addr,
unsigned long, old_len,
unsigned long, new_len,
unsigned long, flags,
void *, new_addr)