Build System leftovers

[eliottness]

• [ ] Rebuild libvpx from conan without the /GL option
• [x] Use the virtualenv generator of conan to use clake and ninja from conan using build_requires
• [x] Use the virtualenvrun generator to make Qt dll avaiblable in the path for holovibes (currently the local install at runtime)
• [ ] Retry to use lld-link (llvm linker) instead of link (MSVC linker) since the blocking point was libvpx

[eliottness]

• [ ] Remove the precompiled header

[eliottness]

• [ ] Setup LTO (Link time optimization)

• https://cmake.org/cmake/help/latest/prop_tgt/INTERPROCEDURAL_OPTIMIZATION.html

• https://cmake.org/cmake/help/latest/module/CheckIPOSupported.html#module:CheckIPOSupported

• https://llvm.org/docs/LinkTimeOptimization.html