libc: remove uses of enum as per #4419

[mbyx]

Description

Removes all uses of enums, replacing them with c_enums. Since c_enums creates numeric types and constants, cfg_attrs were also removed for deriving Copy and Clone. As per #4419

Additionally allow c_enum to take more than one enum as input, similar to the other macros.

Sources

Checklist

• Relevant tests in libc-test/semver have been updated
• No placeholder or unstable values like *LAST or *MAX are
  included (see #3131)
• Tested locally (cd libc-test && cargo test --target mytarget);
  especially relevant for platforms that may not be checked in CI

[rustbot]

Some changes occurred in solarish module

cc @jclulow, @pfmooney