Windows support

[diegoiast]

This is a meta issue to track all the issues needed for a Windows support.

Goals:

1. We aim to support clang-cl. This is the first priority.
2. Later on, cl, from 2022. This is a very low priority.
3. If we manage to get some mingw toolchain to compile the program - I am happy. But this is not a goal.

Problems:

• Some compiler flags are not compatible with clang-cl. (Meta/Windows: fix compilation flags for clang-cl #77)
• We need a package manager to handle building 3rd parties (ICU, fontconfig?, Skia, WABT, more?)
• We need to find an alternative to fontconfig.
• 'sys/time.h' not found
• [[no_unique_address]] not supported (am I using a wrong compiler? I use MSVC 2022 and its clang-cl)
• We need to pull code from previous attempts of this kind of work. (cherry-picks, rebase etc).
• Need to understand how to run the commit linters on the local machine, as we don't want developers to spam the CI/CD with phantom builds, just to fix a typo on the commit log (yes, that is directed at me)

Known forks, branches:

• https://github.com/cammo1123/serenity/tree/WindowsJS2.0
• https://github.com/abuneri/serenity/tree/windows-ladybird

Please do not comment on this issue unless you have something to contribute. This issue is one of the boss-issues - it will take time. Problems and goals will change, nothing is written in stone, provide code if you can.

[asutoshvariar]

Could std::chrono be used as a replacement for the POSIX-only sys/time.h, as it's present in the C++ 20 standard?

[ADKaster]

We have a patch hiding in one of those mentioned branches to make AK::Time and AK::Duration work well on windows, so that's not an issue at the moment.

[seanmiddleditch]

[[no_unique_address]] not supported (am I using a wrong compiler? I use MSVC 2022 and its clang-cl)

A separate msvc::no_unique_address attribute must currently be used instead for ABI reasons: https://devblogs.microsoft.com/cppblog/msvc-cpp20-and-the-std-cpp20-switch/#msvc-extensions-and-abi

This is true in clang-cl too, using a recent-enough version: llvm/llvm-project#65675

[R-Goc]

Why find an alternative to fontconfig? It works on windows and even compiles with clang-cl. It needs to have config files shipped for it as windows doesn't provide any. It is used in GIMP for example.

[niutech]

Have anyone tried to build Ladybird in Cygwin/MSYS2? They provide some POSIX compatibility layer for Windows.

[ADKaster]

As stated in the first post of the issue, Cygwin and Mingw are not a goal. Native windows with clang-cl and wsl2 with wslg are the only two windows configurations we will support in this repository.

[R-Goc]

Maybe a github discussions tab, or other way of collaboration could be opened to avoid spamming this tracking issue. This will need more work. (Also how to get cmake to find ICU data?)