[llvm] [flang] Set compile definitions for flang-rt build on AIX (PR #127919)

[Kelvin Li via llvm-commits]

kkwli wrote:

> Would this otherwise come from
> 
> https://github.com/llvm/llvm-project/blob/0181af2f32e51c2ac45d96bd194884d7adfd10ca/llvm/CMakeLists.txt#L1189
> ?

Yes, it is from there.


https://github.com/llvm/llvm-project/pull/127919