libcommon/files: surround include <sys/syscall> with linux ifdef
#include <sys/mman.h>
#include <sys/socket.h>
#include <sys/stat.h>
+#if defined(_HF_ARCH_LINUX)
#include <sys/syscall.h>
+#endif /* defined(_HF_ARCH_LINUX) */
#include <sys/types.h>
#include <unistd.h>
