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]
{
    double load = 1;
    SeedInsecureRand(SeedRand::ZEROS);
    std::vector<uint256> hashes;
    Cache set{};
    size_t bytes = megabytes * (1 << 20);
    set.setup_bytes(bytes);
    uint32_t n_insert = static_cast<uint32_t>(load * (bytes / sizeof(uint256)));
    hashes.resize(n_insert);
    for (uint32_t i = 0; i < n_insert; ++i) {
        uint32_t* ptr = (uint32_t*)hashes[i].begin();
        for (uint8_t j = 0; j < 8; ++j)
            *(ptr++) = InsecureRand32();
    }
    /** We make a copy of the hashes because future optimizations of the
     * cuckoocache may overwrite the inserted element, so the test is
     * "future proofed".
     */
    std::vector<uint256> hashes_insert_copy = hashes;