wget 1.21.1 fails to build on macOS (10.14, 10.15, 11.1)

[Carlo Cabrera]

wget 1.21.1 fails to build on macOS 10.14, 10.15, and 11.1. The build
fails with a series of errors starting with

    In file included from regex.c:74:
    In file included from ./regexec.c:1362:
    ./malloc/dynarray-skeleton.c:195:13: error: expected identifier or '('
    __nonnull ((1))
                ^
    ./malloc/dynarray-skeleton.c:195:13: error: expected ')'
    ./malloc/dynarray-skeleton.c:195:12: note: to match this '('
    __nonnull ((1))
               ^

Complete build logs available at
    
    https://github.com/Homebrew/homebrew-core/pull/68667

The errors (on 11.1) starts at

    
https://github.com/Homebrew/homebrew-core/pull/68667/checks?check_run_id=1674726970#step:7:910

The exact same errors affect findutils 4.8.0, so the bug may not be in
wget. If so, I'd appreciate being pointed to the right place to submit
this bug report.