[llvm] [flang-rt] Added FLANG_RT_QUADMATH_INCLUDE_DIR option. (PR #130378)

[Slava Zakharin via llvm-commits]

vzakhari wrote:

> Isn't this exactly what `include_directories(${FLANG_RT_QUADMATH_INCLUDE_DIR})` does? Or do you expect users to copy GCC's `quadmath.h` into another directory?
> 
> Better solution here: #130411. No additional configuration input from the user required.

I like your solution better.  Thanks! Let me try it.

https://github.com/llvm/llvm-project/pull/130378