[PATCH] Use 1U everywhere in elf/elf.h.

[Roland McGrath]

> I would like to write a test case for it, but I can't get anything to
> trigger the original reported failure by readelf when running with
> -fsanitize=undefined.
> 
> Therefore I can't at present even get a reproducer nor write a regression
> test, but I know what what we have for SHF_EXCLUDE is wrong.

A regression test for a reported manifest issue is of course worthwhile.
But I was talking about a generic test that verifies at compile time what
the types actually are rather than some particular characteristic of behavior.