Incomplete export of the libraries breaking compiliation for other libraries

[stevefan1999-personal]

Describe the bug
Ditto as title

Environment

• OS: Windows 10 amd64
• Compiler: VS2019/MSVC 14.1

To Reproduce
Steps to reproduce the behavior:

1. Install libtorrent & qt & various boost libraries via vcpkg
2. Clone qbittorrent/qBittorrent and target the CMake build to use vcpkg toolchain
3. Build the generated project using VS2019 under any mode

Expected behavior
It should compile and produce executable artifacts

Failure logs
Except it spams "nope, I can't find some symbols, despite they should have had been exported"

Additional context
Proof of it being an incompletely exported library: Using my fully exported library to fool the compiler but keep the vcpkg originally built DLL in the binary directory, I was getting "entrypoint not found" error, which means the originally built DLL is also (mysteriously) missing this symbol, no wonder why the compiler is complaining back in the IDE.

Thus, I was able to get it working by manually compiling libtorrent with CMAKE_WINDOWS_EXPORT_ALL_SYMBOLS and shimming the DLL with it with this fully exported one.
However, when I was about to make a patch regarding this, I see that in the guideline that adding CMAKE_WINDOWS_EXPORT_ALL_SYMBOLS is disallowed:

Do not add CMAKE_WINDOWS_EXPORT_ALL_SYMBOLS

Unless the author of the library is already using it, we should not use this CMake functionality because it interacts poorly with C++ templates and breaks certain compiler features. Libraries that don't provide a .def file and do not use __declspec() declarations simply do not support shared builds for Windows and should be marked as such with vcpkg_check_linkage(ONLY_STATIC_LIBRARY).

So, we had a dilemma here: We cannot build packages with CMAKE_WINDOWS_EXPORT_ALL_SYMBOLS, yet (maybe the one and only way) to make it work is to use this option.
Yet, libtorrent is impossible to build in static linkage as it creates a huge binary of over 100MB, Nobody wants to wait for half an hour to let it build.
Finally, I suspect there's something wrong with LTCG, or why this would happen will remain a mystery.

[Neumann-A]

Yet, libtorrent is impossible to build in static linkage as it creates a huge binary of over 100MB, Nobody wants to wait for half an hour to let it build.

Install libtorrent & qt & various boost libraries via vcpkg

I feel like this is a contradiction in itself. qt5-base already takes around 30 min to build....
For me it seems more like the compiler flag /Z7 is the real problem of the big binaries.