Restore Windows support with MSVC

[conradoplg]

Same as #38 but with MSVC. It's likely that we'll need to use MSVC since rocksdb only supports it.

[conradoplg]

One of the errors seems related to this https://stackoverflow.com/questions/72907548/expected-c-compiler-error-in-yvals-core-h

[conradoplg]

I managed to get it to work, pending CI. I had to add some ugly workarounds (i.e. comment out some code) in our copy of zcashd that would be get wiped in the next dependency upgrade, so next time I look into this I'll try to sort them out (either manage to remove the workaround, or submit upstream).

In particular, the linking errors are weird. I had to add some files to be compiled in build.rs, but why is it working on Linux then? I'll also investigate this.

Summary of the changes:

• Add a &* to a particular pointer usage in cache.h. It's basically this, so it sounds like something that should be fixed upstream.
• Rename generated .c files to .cpp, because MSVC uses the file extension to choose the compiler.
• Add amount.cpp, zip317.cpp and cache.cpp. No idea why that's not needed on Linux?
• Comment a logging line in cache.cpp along with an include, which would otherwise require vendoring boost/filesystem

[conradoplg]

• Add a &* to a particular pointer usage in cache.h. It's basically this, so it sounds like something that should be fixed upstream.

Created zcash/zcash#6835

• Add amount.cpp, zip317.cpp and cache.cpp. No idea why that's not needed on Linux?

I looked into this a bit but couldn't find a good explanation quickly. It seems easier to just ignore it. My hunch is that is something related to differences between Linux and Windows linking. Maybe these unresolved symbols in Windows are not actually being used in the final binary, and in Linux it's smart enough to detect that and ignore them.

• Comment a logging line in cache.cpp along with an include, which would otherwise require vendoring boost/filesystem

In the end I left the manual patch and committed a patch file and instructions on how to patch the zcash source when it's updated.

[oxarbitrage]

It seems to be working and looks good to me. I was wondering if we can just remove the commented lines in cache.cpp and in the patch.

[mpguerra]

We might want to do that in a follow up PR if we just want to get this working and released now

[mpguerra]

@gustavovalverde once this merges I think we can re-enable all windows tests again