[llvm] [mlir] Config: Move LLVM_HAS_*_TARGET definitions to a new header. (PR #136388)

[Sergei Barannikov via llvm-commits]

s-barannikov wrote:

I'm strongly in favor of this change. I often enable/disable targets and it results in rebuilding everything.
ccache helps, but it still runs the preprocessing step (I think), which isn't quite fast. Also, any change in target list results in llvm-tblgen trying to rebuild all the generated files, which is even slower.


https://github.com/llvm/llvm-project/pull/136388