[llvm] [llvm-c] Create a 128 bit floating point constant from 2 64 bit values (PR #164381)

[Nikita Popov via llvm-commits]

nikic wrote:

> I'm not sure where to place these tests, ie Core.cpp tests in general.

In this case probably https://github.com/llvm/llvm-project/blob/main/llvm/unittests/IR/ConstantsTest.cpp.
 
> I agree a generic initializer would make more sense but that kind of C++ expertise is a bit beyond me I'm afraid.

I think it would look similar to what you have now, but accept the type as an argument and call `getFltSemantics()` on it instead of hardcoding `APFloat::IEEEquad()`.

https://github.com/llvm/llvm-project/pull/164381