[clang] [llvm] Enable ClangIR Build By Default (PR #221291)

[Erich Keane via cfe-commits]

erichkeane wrote:

> Can you please make sure this works with the dylib build?
> 
> Currently this fails to link for the full build, and if you build just clang the binary is completely broken.

Oh!  Thank you for pointing that out!  I am/was unaware of this.  I'll have to figure out how to do this. I'll definitely  make sure it works before merging. 

https://github.com/llvm/llvm-project/pull/221291