[llvm] Workflows: Drop Windows release builds and use more powerful runners for others (PR #117111)

[Tom Stellard via llvm-commits]

tstellar wrote:

I went ahead and dropped the multi-stage builds, so this workflow file is much more simple now.  Linux/X86 and Mac/AArch64 will use depot runners and Mac/X86 will use larger github runners.  However, to save resources, the Mac builds will use the free runners when testing pull requests.

https://github.com/llvm/llvm-project/pull/117111