[llvm] cmake: Avoid using if(TARGET x AND TARGET y) (PR #159707)

[Matt Arsenault via llvm-commits]

arsenm wrote:

I was trying to fix the last build error, and figured the targets didn't exist. It turns out they do exist, just aren't executable. so yes probably should drop the target checks 

https://github.com/llvm/llvm-project/pull/159707