Make compile with msvc, clang and gcc on Windows

[oltolm]

I added support for compiling rpcs3 with msvc, clang and gcc on Windows using cmake. I also fixed some compilation errors and warnings and cleaned up some cmake scripts. I tested it on Windows and Linux.

On Windows you can use clang in the msys2 clang64 environment or gcc in the msys2 mingw64 environment. See https://www.msys2.org/docs/environments/.

You can generate a VS solution with:

cmake --preset msvc -DQt5_DIR=<path to Qt5 directory>

I realize that there are a lot of changes. I guess I could reduce the amount of changes by disabling some warning instead of fixing them.

[kd-11]

Added some comments. Something to keep in mind - we support building on anemic CI machines so some blocks guarded by __AVX__ or __RTM__ may be missing on released builds. Also we cannot globally enable these because we support some really ancient processors and compilers may inject unsupported bytecode during optimization passes. There were some optimizations that was locked behind an AVX check and this actually made release builds slower than self-compiled which is a pre-existing problem.

[Nekotekina]

Some missing stat() changes in File.cpp

[Nekotekina]

But overall, LGTM