/usr/mipsel-linux-gnu/include/bits/a.out.h is in libc6-dev-mipsel-cross 2.27-3ubuntu1cross1.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 3 4 5 6 7 | #ifndef __A_OUT_GNU_H__
# error "Never use <bits/a.out.h> directly; include <a.out.h> instead."
#endif
/* Signal to users of this header that this architecture really doesn't
support a.out binary format. */
#define __NO_A_OUT_SUPPORT 1
|