validation: Check absence of locks at compile-time (LOCKS_EXCLUDED) in addition to the current run-time checking (AssertLockNotHeld) #15721

Check absence of locks at compile-time (using LOCKS_EXCLUDED annotation) in addition to the current run-time checking (using AssertLockNotHeld(…)).

In line with the developer notes:

Generally; compile-time checking is preferred over run-time checking.

For people who are not compiling with clang -Werror=thread-safety-analysis -- this is the type of checking these annotations enable:

[…]: error: cannot call function 'LimitValidationInterfaceQueue' while mutex 'cs_main' is
     held [-Werror,-Wthread-safety-analysis]
            LimitValidationInterfaceQueue();
            ^

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The following sections might be updated with supplementary metadata relevant to reviewers and maintainers.

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Conflicts

Reviewers, this pull request conflicts with the following ones:

• #15921 (Tidy up ValidationState interface by jnewbery)

If you consider this pull request important, please also help to review the conflicting pull requests. Ideally, start with the one that should be merged first.

FWIW: I've verified that a disassembly of the bitcoind binary built on a Ubuntu 18.04 machine with this patch applied is identical to a disassembly of the bitcoind binary built against master (as expected).

Oh, forgot that I submitted this PR back in April. Replaced by #15967 submitted earlier today which covers a few more functions. See also #15967.