Apple started the Clang project buddy, you’ve got your cause and effect backwards.

Yes, because they weren't willing to keep using their GCC fork, for various reason, namely the license (which already made Steve Jobs unhappy once), and being less modular (as per design decision).

It's also usable as a library in a way GCC isn't. That's why Apple started using it with their OpenGL software drivers back in the day. That's why almost all modern and new programming languages use LLVM, and those that don't do not use GCC.

Even if GCC was easily usable as library, many of those LLVM use cases don't work that well with GCC's license.

That's out of date, libgccjit exists. LLVM is a bit difficult to use as a library because it has no stable API and is in C++ so it doesn't have a stable ABI either.

LLVM does offer a C based stable ABI, even though it isn't as feature rich as the C++ one, is good enough for most use cases.

https://llvm.org/doxygen/group__LLVMC.html

Hmm.. why is it called "jit"? That seems like it's telling everyone the use case is very different from LLVM. Also the big EXPERIMENTAL banner doesn't instill confidence. Unlike with LLVM which is used by dozens of production languages.

Why would you need it as a library other than to do jit?

Actually GCC for Windows target is like pain in the ass. Look for how many problems ReactOS had with it. Also this would need SEH to be implemented. Clang gives that out of the box.

Don't care for legacy dying OS's, sorry.