ujail: elf: work around GCC bug on MIPS64

ujail: elf: work around GCC bug on MIPS64

Work-around gcc bug which leads to segfault parsing ELF on MIPS64.
The codepath added in this commit gets triggered when parsing
/lib/ld-musl-mips64-sf.so.1 (a symlink to /lib/libc.so) on MIPS64
(built with gcc-8.4.0 and musl 1.1.24) in qemu-system-mips64 on the
malta/be64 target.
Include work-around outputting an error message, but preventing
segfault when building for MIPS64.

Tested-by: Roman Kuzmitskii <damex.pp@icloud.com>
[tested on edgerouter 4 and edgerouter lite]
Signed-off-by: Daniel Golle <daniel@makrotopia.org>