[clang] [clang] Remove FEM_Indeterminable (PR #137247)

[Aaron Ballman via cfe-commits]

AaronBallman wrote:

> I've reverted, not sure why I thought it had been reviewed?

Thanks! And I'm happy enough blaming GitHub's poor Ux for all confusion. :-)

@zahiraam -- any chance you can look into this?

https://github.com/llvm/llvm-project/pull/137247