madvise: tolerate EINVAL and ENOSYS when minherit fails

[nmathewson]

These errors can occur if we are built on a system with support for
madvise(MADV_NOFORK) but then we are run on a system whose kernel
does not support that flag.

If the error is something that we don't tolerate at all, we now log
it before crashing.

Fixes bug 31696. I am calling this a bugfix on 0.4.1.1-alpha, where
we actually started using the map_anon code.

This is similar to, but not the same as, the fix for #31570.

[coveralls]

Pull Request Test Coverage Report for Build 6159

• 1 of 4 (25.0%) changed or added relevant lines in 1 file are covered.
• 13 unchanged lines in 3 files lost coverage.
• Overall coverage decreased (-0.02%) to 62.613%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
src/lib/malloc/map_anon.c	1	4	25.0%

Files with Coverage Reduction	New Missed Lines	%
src/feature/hs/hs_service.c	1	73.32%
src/feature/dirauth/shared_random.c	3	85.54%
src/feature/dirauth/dirvote.c	9	64.74%

Totals
Change from base Build 6068:	-0.02%
Covered Lines:	46929
Relevant Lines:	74951

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💛 - Coveralls