Build CVC{4,5} natively on Windows

[RyanGlScott]

This patch:

• Upgrades CVC5 to version 1.0.5, which contains several key bugfixes and a new --win64-native flag, which allows CVC5 to be build natively on Windows.
• Backports the --win64-native flag to CVC4, thereby allowing it to be built natively as well.
• Tweaks the CI configuration to clean up how Python dependencies are installed, which are important to building CVC4 and CVC5.

Fixes https://github.com/GaloisInc/what4-solvers/issues/4. By upgrading the CVC5 version, this also fixes https://github.com/GaloisInc/what4-solvers/issues/31.