Happens on all recent builds. Seemingly unrelated to any code changes.

Last pass: https://ci.appveyor.com/project/DrahtBot/bitcoin/builds/30240770
First fail: https://ci.appveyor.com/project/DrahtBot/bitcoin/builds/30241275
First fail on master: https://ci.appveyor.com/project/DrahtBot/bitcoin/builds/30241926

The first fail happened on the 0.19 branch. Is the appveyor cache shared across branches?

Otherwise it could be a msvc update or another dependency that broke it. If so, I wish we figure out a way to freeze the dependencies and compileres in some way.


```
C:\projects\bitcoin\src\test\cuckoocache_tests.cpp(330,10): error C2976: 'std::deque': too few template arguments [C:\projects\bitcoin\build_msvc\test_bitcoin\test_bitcoin.vcxproj]
C:\projects\bitcoin\src\test\cuckoocache_tests.cpp(330,1): error C2079: 'last_few' uses undefined class 'std::deque' [C:\projects\bitcoin\build_msvc\test_bitcoin\test_bitcoin.vcxproj]
C:\projects\bitcoin\src\test\cuckoocache_tests.cpp(341,1): error C2672: 'begin': no matching overloaded function found [C:\projects\bitcoin\build_msvc\test_bitcoin\test_bitcoin.vcxproj]
C:\projects\bitcoin\src\test\cuckoocache_tests.cpp(341,1): error C2893: Failed to specialize function template 'unknown-type std::begin(_Container &)' [C:\projects\bitcoin\build_msvc\test_bitcoin\test_bitcoin.vcxproj]
C:\projects\bitcoin\src\test\cuckoocache_tests.cpp(341,1): error C2784: 'const _Elem *std::begin(std::initializer_list<_Elem>) noexcept': could not deduce template argument for 'std::initializer_list<_Elem>' from 'int' [C:\projects\bitcoin\build_msvc\test_bitcoin\test_bitcoin.vcxproj]
C:\projects\bitcoin\src\test\cuckoocache_tests.cpp(341,1): error C2672: 'end': no matching overloaded function found [C:\projects\bitcoin\build_msvc\test_bitcoin\test_bitcoin.vcxproj]
C:\projects\bitcoin\src\test\cuckoocache_tests.cpp(341,1): error C2893: Failed to specialize function template 'unknown-type std::end(_Container &)' [C:\projects\bitcoin\build_msvc\test_bitcoin\test_bitcoin.vcxproj]
C:\projects\bitcoin\src\test\cuckoocache_tests.cpp(341,1): error C2784: 'const _Elem *std::end(std::initializer_list<_Elem>) noexcept': could not deduce template argument for 'std::initializer_list<_Elem>' from 'int' [C:\projects\bitcoin\build_msvc\test_bitcoin\test_bitcoin.vcxproj]
C:\projects\bitcoin\src\test\cuckoocache_tests.cpp(341,1): error C3536: '<begin>$L0': cannot be used before it is initialized [C:\projects\bitcoin\build_msvc\test_bitcoin\test_bitcoin.vcxproj]
C:\projects\bitcoin\src\test\cuckoocache_tests.cpp(341,1): error C3536: '<end>$L0': cannot be used before it is initialized [C:\projects\bitcoin\build_msvc\test_bitcoin\test_bitcoin.vcxproj]
C:\projects\bitcoin\src\test\cuckoocache_tests.cpp(341,1): error C2100: illegal indirection [C:\projects\bitcoin\build_msvc\test_bitcoin\test_bitcoin.vcxproj]
for (uint32_t i = 0; i < (n_insert / 2); ++i)
        set.insert(hashes_insert_copy[i]);
    
    for (uint32_t i = 0; i < (n_insert / 4); ++i)
        BOOST_CHECK(set.contains(hashes[i], true));
    
    for (uint32_t i = (n_insert / 2); i < n_insert; ++i)
        set.insert(hashes_insert_copy[i]);
    
    size_t count_erased_but_contained = 0;
    
    size_t count_stale = 0;
    
    size_t count_fresh = 0;
    for (uint32_t i = 0; i < (n_insert / 4); ++i)
        count_erased_but_contained += set.contains(hashes[i], false);
    for (uint32_t i = (n_insert / 4); i < (n_insert / 2); ++i)
        count_stale += set.contains(hashes[i], false);
    for (uint32_t i = (n_insert / 2); i < n_insert; ++i)
        count_fresh += set.contains(hashes[i], false);
    double hit_rate_erased_but_contained = double(count_erased_but_contained) / (double(n_insert) / 4.0);
    double hit_rate_stale = double(count_stale) / (double(n_insert) / 4.0);
    double hit_rate_fresh = double(count_fresh) / (double(n_insert) / 2.0);
    
    BOOST_CHECK_EQUAL(hit_rate_fresh, 1.0);
    
    
    BOOST_CHECK(hit_rate_stale > 2 * hit_rate_erased_but_contained);
}
BOOST_AUTO_TEST_CASE(cuckoocache_erase_ok)