Add 64-bit job to Appveyor

This adds SDL and DD 64-bit builds to Appveyor. I use x86_64 GCC 7.3.0, located in C:\mingw-w64\x86_64-7.3.0-posix-seh-rt_v5-rev0\mingw64.

I also disable UPX by default, because we're not using that for release builds due to virus scan issues. The user can override this by setting NOUPX=0 in Appveyor's project settings.

This requires !440 (merged) to be merged because that MR handles MINGW64 earlier in the Makefile, which avoids a compile error.

Results and artifacts: https://ci.appveyor.com/project/mazmazz/srb2/builds/21290671

mentioned in merge request KartKrew/Kart-Public!7 (merged)

added 4 commits

• 941e2978 - Implement install building for appveyor (deployer)
• e1300d51 - Rename ASSET_PATCH_DLL_GET to PACKAGE_PATCH_DLL_GET
• f00cfb7b - Use optional asset archive instead of file
• bd81c319 - Merge branch 'appveyor-deployer' into 'appveyor-64'

Compare with previous version

merged

mentioned in commit ce7875b1