[libc] [llvm] [libc][math][c23] Add fmaf16 C23 math function. (PR #130757)

[Harrison Hao via llvm-commits]

harrisonGPU wrote:

Hi, @lntue @overmighty ,  I found an issue with the FMA tests. When we enable the fmaf16 type test, the values of IN_MAX_SUBNORMAL_U and IN_MIN_SUBNORMAL_U are 1023 and 1 respectively:
https://github.com/llvm/llvm-project/blob/2a4522229c7b744dcd268a790ba61e4eb2bfa315/libc/test/src/math/FmaTest.h#L37-L46
If we calculate the step as follows:
```
constexpr InStorageType STEP =
        (IN_MAX_SUBNORMAL_U - IN_MIN_SUBNORMAL_U) / COUNT;
```
this will result in STEP being zero due to integer division, causing the loop condition never to be met and the loop to run indefinitely:
https://github.com/llvm/llvm-project/blob/2a4522229c7b744dcd268a790ba61e4eb2bfa315/libc/test/src/math/FmaTest.h#L64-L73,
I have made some modifications in this PR to address this issue. Could you please take a look? :-)


https://github.com/llvm/llvm-project/pull/130757